Russian space officials are warning that the international space station will have to be mothballed unless the United States or another partner in the huge project comes up with $100 million to pay for more Russian spacecraft to supply a skeleton crew on the station.

Alexei Krasnov, deputy head of international cooperation for the Russian space agency, Rosaviakosmos, said in an interview that Russia alone has been called on to keep the football field-sized station supplied after NASA grounded its three remaining shuttles last month. But "no one has come up with a suggestion on how to procure the funds" for extra supply ships required, he said.

Russia's assessment contrasted with a more positive picture than NASA officials have been painting of the space station's future following last month's loss of the shuttle Columbia.

NASA Administrator Sean O'Keefe told a congressional panel two weeks ago that the 16-nation coalition that backs the space station has agreed that Russia will provide two more unmanned Progress cargo spacecraft to ferry water, fuel and necessities to the station for the next 18 months. That would enable a reduced crew of two to maintain the station in orbit while NASA investigates the Columbia accident, which killed seven astronauts, he said.

But Krasnov said in an interview that the financing for the additional Russian supply ships, which cost about $50 million each, including booster rockets, is nowhere in sight. Time is fast running out, he said, if Russia is to complete a Progress spacecraft to keep the station supplied this year and begin work on another to fly next year. It takes a minimum of 18 months to build the craft, he said.

"We need to start now," said Krasnov. "We are under terrific time pressure."

A NASA spokesman said today he could not immediately comment on Krasnov's remarks.

With an annual $270 million budget for its space program, Russia is struggling to fulfill even its current responsibilities with the space station. Even as it devotes half of that money to the international project, the Russian agency can little more than serve as its coachman, ferrying crews and supplies to and from Earth, the agency's director, Yuri Koptev, said in December.

Because of the new pressure on resources that followed the loss of Columbia, Russia has canceled commercial and space tourist flights that would have brought in $31 million this year, according to Krasnov. Not a ruble is left for extra supply flights, he said.

President Vladimir Putin refused last month to give the agency more funds to service the space station, saying the agency should seek financial contributions from the 15 other partners in the project, he said.

The United States, the project coordinator with an annual $14.7 billion space budget, is the most likely candidate. But O'Keefe testified last month that he saw no need for the United States to finance more Russian spacecraft, on the grounds that other partners in the project were shouldering the burden. For instance, he said, the European Space Agency agreed to pay Russia to ferry two European astronauts to the space station, even though their flights have been delayed because of the shuttle disaster.

But Krasnov said that while the European contribution will help Russia carry out its added responsibilities, it still leaves it $100 million short. Japan and Canada, two other partners, have already declined to contribute more funds, he said.

How to get water, fuel and other necessities to the crew has been the most critical question facing the international space station since the Columbia shuttle disintegrated over Texas on Feb. 1. Shuttles can deliver 100 tons of cargo each, including the large-scale equipment needed to continue construction of the $96 billion station. The Progress freighter can carry at most 21/2 tons.

That has already forced the project's partners to make plans to cut the current three-man crew down to two astronauts, whose jobs will be mainly maintenance, with a bare minimum of research. A Russian cosmonaut and American astronaut are now training at a center outside Moscow to replace the current crew, mostly likely in early May.

Neither the Americans nor the Russians want to leave the station unmanned and risk a malfunction that could not be corrected from the ground. The project's partners, led by the United States, have already invested $16 billion to $18 billion, Krasnov said. "The option to fly the station without a crew is absolutely not desirable," he said.

Space station Expedition Commander Ken Bowersox, right, stows his upper suit in an airlock without help from Science Officer Donald Pettit in an exercise Feb. 24 to explore the feasibility of a two-person crew.