Worried that trouble in Moscow is threatening its own dreams, NASA wants to spend up to $660 million over five years to bail out its Russian partner in building a planned international space station, agency officials said Monday.

Key members of Congress immediately faulted the proposal as too expensive, clouding the fate of the biggest science project of all time. But NASA officials argued that the American and Russian programs are now linked so intimately that the Russian effort must be preserved lest the American space program suffer.In just two months, orbital construction is to start on the sprawling outpost for astronauts, which is expected to cost more than $40 billion. But even if the new bailout goes through and keeps the Russians afloat, the station project is facing another round of construction delays next year because of Russia's problems in building a key part. The lag in that work will also have costly repercussions for the nation's fleet of space shuttles, which are to carry station elements into orbit.

Already, past delays have cut the flight rate of the winged spaceships to unusually low levels, and NASA officials are scrambling to find new shuttle payloads to compensate for looming gaps in outpost construction.

Joseph Rothenberg, associate administrator for space flight at the National Aeronautics and Space Administration, said that the new bid to save the Russians and the beleaguered outpost is likely to cost about $1.2 billion, including the new money for the Russians as well as about $540 million in new American work such as modifying the shuttles so they can do more station lifting.

Rothenberg said the space agency had already squeezed its own $13.6 billion budget as far as possible to find emergency funds for the outpost's rescue, and that it was eager for new money.

The $1.2 billion in emergency money, Rothenberg said, was much cheaper than losing Moscow's help altogether. "Any alternative you look at without the Russians would hit the program hard," hesaid.

But top members of Congress are questioning the new bailout.

"Given NASA's track record, we are justifiably concerned and skeptical," said Sen. John McCain, R-Ariz., chairman of the Senate Commerce Committee, which oversees NASA.

Some critics go further, saying NASA officials should put the whole station project on indefinite hold.

"They're trying to stick with a failed strategy," said James Oberg, an American expert on the Russian space program. He said the station's delays threatened to add billions of dollars in hidden costs to NASA's shuttle operations. "Next year's shuttle schedule is entirely up in the air."