America's crippled human spaceflight program, unable to count on flying the space shuttle, could lose the use of Russian spacecraft as well within a few weeks, forcing U.S. astronauts to abandon the international space station and effectively grounding them for the foreseeable future.

To forestall this possibility, the Bush administration is seeking to eliminate a provision in the 2000 Iran Nonproliferation Act prohibiting U.S. purchases of most Russian space technology and equipment -- including Soyuz spacecraft -- as long as Russia is exporting nuclear or missile technology or know-how to Iran.

Congress is prepared to amend the law, but there is no agreement yet on how broad the amendment should be, and hard-line congressional critics of Iran might affect the fate of the legislation.

Yesterday, Senate Foreign Relations Committee Chairman Richard G. Lugar (R-Ind.) introduced a bill amending the law to allow both NASA and U.S. corporations to purchase Russian space equipment until 2012.

Lugar is seeking advance approval from all 100 senators so the measure can pass unanimously. The House is working on similar legislation for a floor vote perhaps next week. Senate and House aides expressed confidence that a joint measure will eventually win approval.

If it does not, President Bush could get around the prohibition by certifying that Russia is not violating the nonproliferation law, but a senior administration official said yesterday that Bush will not grant such a waiver. Bush is expected to discuss Iran when he meets with Russian President Vladimir Putin today.

Unless Congress or the president acts, no U.S. astronaut will have access to space after the Soyuz flight scheduled to fly to the station on Sept. 30. The shuttle was grounded again after the flight of Discovery resulted in renewed foam-shedding problems.

The dilemma is a fresh example of how the 2003 Columbia tragedy has curtailed U.S. spaceflight and forced a dependence on Russia, even as Bush urges NASA to embark on a new national initiative to send humans back to the moon by 2020 and eventually to Mars.

"This has been coming for years, and now we're facing the crisis," said Rep. Dana Rohrabacher (R-Calif.), an author of the 2000 law who now favors amending it. "I don't like it, but it's a choice of being dependent on the Russians or dependent on the space shuttle, and it's becoming more and more apparent that it's riskier to depend on the space shuttle."

But Rep. Brad Sherman (D-Calif.), like Rohrabacher an anti-Iran hard-liner and a member of both the House Science and Foreign Relations committees, said "there is no need for an amendment" because "it sends the message that there will be no consequences for violating the [nonproliferation] act." The amendment "would be dead on arrival," he said, if "the House weren't a rubber stamp for this administration."

The shuttle is grounded until at least March and probably longer to correct defects in the external fuel tank and to overcome the effects of Hurricane Katrina at NASA installations in New Orleans and Mississippi, two facilities critical to shuttle operations.

William H. Gerstenmaier, NASA's associate administrator for space operations, said in a news conference last week that the United States intends to have a "plan in place" for continued cooperation with Russia before sending astronaut William S. McArthur Jr. to the space station on Sept. 30.

Dean Acosta, spokesman for NASA Administrator Michael D. Griffin, said the agency is "very, very confident that we will be able to work with any agreement that comes about between the administration and Congress." He acknowledged "there is an urgency" in resolving the issue.

Rohrabacher said NASA has told Congress that unless a solution is found, Russia will not begin the October training for the U.S. astronaut assigned to replace McArthur in April.

"Desperate is too strong a word," said one knowledgeable Republican congressional aide of the administration's interest in amending the law. "But they're getting real nervous. The Russians have told them [NASA] they will not give the astronaut a visa."

This source and other congressional aides agreed to speak about efforts to amend the act on the condition of anonymity, either because discussions are still developing or because the lawmakers they work for have not yet taken a position.

The Iran Nonproliferation Act was conceived by a Republican Congress to stiffen President Bill Clinton's resolve in responding to Russian support for Iran's nuclear ambitions. The prohibition on purchases of Russian space technology has never taken effect because a previous agreement obligated the Russians to provide 11 free Soyuz flights for U.S. astronauts staffing the space station. The Sept. 30 flight will be the 11th.

Russia has warned for several years that it would require payment for further flights. Its cash-strapped space program has charged two space tourists an estimated $20 million apiece for a visit to the station and is scheduled to take New Jersey entrepreneur Gregory Olsen on Sept. 30, along with McArthur and Russian flight engineer Valery I. Tokarev.

On July 12, Griffin sent Congress a proposed Nonproliferation Act amendment that would effectively allow the administration to buy Russian space technology for any purpose and for as long as it is needed.

Rohrabacher said he supports the administration proposal because the sanctions have not worked and Russia has "already made the contributions they're going to make to the Iran nuclear program."

His view does not appear to have widespread support, however, both because of congressional antipathy toward Iran and concern that continued reliance on Soyuz could lead to Russian price-gouging and could short-circuit NASA's efforts to develop its own next-generation space vehicle.

"Everyone's willing to give them what they need for the next few [Soyuz] flights," one Republican House aide said. "But there's a fair amount of debate on anything beyond that or whether to allow private contractors to make deals."

Still, there appears to be no organized opposition. "I would know if there was," said Rep. Howard L. Berman (D-Calif.), a senior member of the House International Relations Committee and a noted anti-Iran hawk. "But we're on the horns of a dilemma here. I want a narrow fix -- to use Soyuz to bring people up and down. That's all."

The shuttle Atlantis is grounded until at least March because of fuel-tank defects. NASA also needs to repair installations damaged by Katrina. Sen. Richard Lugar backs the purchase of Russian hardware.