{See the Disclosure Project Website for more information on the Space Weapon Program. We are probably going to see more UFO activity from now on. Wes Penre)

The Air Force, saying it must secure space to protect the nation from attack, is seeking President Bush's approval of a national-security directive that could move the United States closer to fielding offensive and defensive space weapons, according to White House and Air Force officials.

The proposed change would be a substantial shift in American policy. It would almost certainly be opposed by many American allies and potential enemies, who have said it may create an arms race in space.

A senior administration official said that a new presidential directive would replace a 1996 Clinton administration policy that emphasized a more pacific use of space, including spy satellites' support for military operations, arms control and nonproliferation pacts.

Any deployment of space weapons would face financial, technological, political and diplomatic hurdles, although no treaty or law bans Washington from putting weapons in space, barring weapons of mass destruction.

A presidential directive is expected within weeks, said the senior administration official, who is involved with space policy and insisted that he not be identified because the directive is still under final review and the White House has not disclosed its details.

Air Force officials said yesterday that the directive, which is still in draft form, did not call for militarizing space. "The focus of the process is not putting weapons in space," said Maj. Karen Finn, an Air Force spokeswoman, who said that the White House, not the Air Force, makes national policy. "The focus is having free access in space."

With little public debate, the Pentagon has already spent billions of dollars developing space weapons and preparing plans to deploy them.

"We haven't reached the point of strafing and bombing from space," Pete Teets, who stepped down last month as the acting secretary of the Air Force, told a space warfare symposium last year. "Nonetheless, we are thinking about those possibilities."

In January 2001, a commission led by Donald H. Rumsfeld, then the newly nominated defense secretary, recommended that the military should "ensure that the president will have the option to deploy weapons in space."

It said that "explicit national security guidance and defense policy is needed to direct development of doctrine, concepts of operations and capabilities for space, including weapons systems that operate in space."

The effort to develop a new policy directive reflects three years of work prompted by the report. The White House would not say if all the report's recommendations would be adopted.

In 2002, after weighing the report of the Rumsfeld space commission, President Bush withdrew from the 30-year-old Antiballistic Missile Treaty, which banned space-based weapons.

Ever since then, the Air Force has sought a new presidential policy officially ratifying the concept of seeking American space superiority.

The Air Force believes "we must establish and maintain space superiority," Gen. Lance Lord, who leads the Air Force Space Command, told Congress recently. "Simply put, it's the American way of fighting." Air Force doctrine defines space superiority as "freedom to attack as well as freedom from attack" in space.

The mission will require new weapons, new space satellites, new ways of doing battle and, by some estimates, hundreds of billions of dollars. It faces enormous technological obstacles. And many of the nation's allies object to the idea that space is an American frontier.

Yet "there seems little doubt that space-basing of weapons is an accepted aspect of the Air Force" and its plans for the future, Capt. David C. Hardesty of the Naval War College faculty says in a new study.

A new Air Force strategy, Global Strike, calls for a military space plane carrying precision-guided weapons armed with a half-ton of munitions. General Lord told Congress last month that Global Strike would be "an incredible capability" to destroy command centers or missile bases "anywhere in the world."

Pentagon documents say the weapon, called the common aero vehicle, could strike from halfway around the world in 45 minutes. "This is the type of prompt Global Strike I have identified as a top priority for our space and missile force," General Lord said.

The Air Force's drive into space has been accelerated by the Pentagon's failure to build a missile defense on earth. After spending 22 years and nearly $100 billion, Pentagon officials say they cannot reliably detect and destroy a threat today.

"Are we out of the woods? No," Lt. Gen. Trey Obering, who directs the Missile Defense Agency, said in an interview. "We've got a long way to go, a lot of testing to do."

While the Missile Defense Agency struggles with new technology for a space-based laser, the Air Force already has a potential weapon in space.

In April, the Air Force launched the XSS-11, an experimental microsatellite with the technical ability to disrupt other nations' military reconnaissance and communications satellites.

Another Air Force space program, nicknamed Rods From God, aims to hurl cylinders of tungsten, titanium or uranium from the edge of space to destroy targets on the ground, striking at speeds of about 7,200 miles an hour with the force of a small nuclear weapon.

A third program would bounce laser beams off mirrors hung from space satellites or huge high-altitude blimps, redirecting the lethal rays down to targets around the world. A fourth seeks to turn radio waves into weapons whose powers could range "from tap on the shoulder to toast," in the words of an Air Force plan.

Captain Hardesty, in the new issue of the Naval War College Review, calls for "a thorough military analysis" of these plans, followed by "a larger public debate."

"To proceed with space-based weapons on any other foundation would be the height of folly," he concludes, warning that other nations not necessarily allies would follow America's lead into space.

Despite objections from members of Congress who thought "space should be sanctified and no weapons ever put in space," Mr. Teets, then the Air Force under secretary, told the space-warfare symposium last June that "that policy needs to be pushed forward."

Last month, Gen. James E. Cartwright, who leads the United States Strategic Command, told the Senate Armed Services nuclear forces subcommittee that the goal of developing space weaponry was to allow the nation to deliver an attack "very quickly, with very short time lines on the planning and delivery, any place on the face of the earth."

Senator Jeff Sessions, a Republican from Alabama who is chairman of the subcommittee, worried that the common aero vehicle might be used in ways that would "be mistaken as some sort of attack on, for example, Russia."

"They might think it would be a launch against them of maybe a nuclear warhead," Senator Sessions said. "We want to be sure that there could be no misunderstanding in that before we authorize going forward with this vehicle."

General Cartwright said that the military would "provide every opportunity to ensure that it's not misunderstood" and that Global Strike simply aimed to "expand the choices that we might be able to offer to the president in crisis."

Senior military and space officials of the European Union, Canada, China and Russia have objected publicly to the notion of American space superiority.

They think that "the United States doesn't own space - nobody owns space," said Teresa Hitchens, vice president of the Center for Defense Information, a policy analysis group in Washington that tends to be critical of the Pentagon. "Space is a global commons under international treaty and international law."

No nation will "accept the U.S. developing something they see as the death star," Ms. Hitchens told a Council on Foreign Relations meeting last month. "I don't think the United States would find it very comforting if China were to develop a death star, a 24/7 on-orbit weapon that could strike at targets on the ground anywhere in 90 minutes."

International objections aside, Randy Correll, an Air Force veteran and military consultant, told the council, "the big problem now is it's too expensive."

The Air Force does not put a price tag on space superiority. Published studies by leading weapons scientists, physicists and engineers say the cost of a space-based system that could defend the nation against an attack by a handful of missiles could be anywhere from $220 billion to $1 trillion.

Richard Garwin, widely regarded as a dean of American weapons science, and three colleagues wrote in the March issue of IEEE Spectrum, the professional journal of electric engineering, that "a space-based laser would cost $100 million per target, compared with $600,000 for a Tomahawk missile."

"The psychological impact of such a blow might rival that of such devastating attacks as Hiroshima," they wrote. "But just as the unleashing of nuclear weapons had unforeseen consequences, so, too, would the weaponization of space."

Surveillance and reconnaissance satellites are a crucial component of space superiority. But the biggest new spy satellite program, Future Imagery Architecture, has tripled in price to about $25 billion while producing less than promised, military contractors say. A new space technology for detecting enemy launchings has risen to more than $10 billion from a promised $4 billion, Mr. Teets told Congress last month.

But General Lord said such problems should not stand in the way of the Air Force's plans to move into space.

"Space superiority is not our birthright, but it is our destiny," he told an Air Force conference in September. "Space superiority is our day-to-day mission. Space supremacy is our vision for the future."