NASA managers yesterday said they have stopped work on a series of science projects and an underwater training facility as their first response to new congressional restrictions on the proposed international space station.

They have also directed the companies they have hired to build the station to "unfetter their minds," and even disagree with their NASA bosses in developing ways to simplify or eliminate elements of the project.

Congress has given NASA 90 days to come up with a plan that strips $6 billion out of the space station plan over the next five years and stretches out the project to keep yearly expenditures within specified ceilings. Thousands of jobs are expected to be lost.

The lawmakers also ordered the facility broken into a series of self-sufficient phases, beginning with an orbiting platform that would be visited several times a year by shuttle astronauts for a couple of weeks at a time, to do research on the effects of weightlessness on various materials. This phase would require a shuttle docked to the space station to provide life support for the astronauts in orbit.

William B. Lenoir, head of NASA's office of manned space flight, said the space agency is just beginning the reassessment, which is expected to be completed Jan. 22.

"That's our challenge, to take $6 billion out of the program over the next five years and maintain a useful, affordable, desirable space station program," Lenoir said.

"If we cannot come up with what we consider to be a reasonable program" that retains NASA's top two priorities -- facilities for research on life sciences, leading to a permanently manned orbiting laboratory, as well as research on materials in weightlessness -- then "we would have to readdress whether we can go forward with the space station."

If budget constraints limit the space station only to research on the effect of weightlessness on materials, "this is not a clever way to spend the country's money," he said.

If the design does move ahead, he said, the target date for beginning construction in orbit is March 1995. The capability to permanently house four to eight astronauts, who will stay aboard 90 days at a time, has been delayed until sometime after the year 2000.

The restructuring will save as much as possible of the existing design, officials said. Lenoir said the international partners in the station -- the European Space Agency, Japan and Canada -- will be consulted fully, although they are "uniformly disappointed" at the need to restructure the project. He also said the administration may decide to fight the budget limits.

The space station program employs about 10,000 workers around the country. Lenoir said there is a difference of 2,000 jobs between the $2.1 billion spending level at which the program had been operating and the $1.9 billion level of its new budget.

NASA was already considering halving the size of the laboratory and living modules, enabling them to be carried fully assembled in the shuttle cargo bay. Eventually the space agency might double the number of modules to recover the lost volume. The support beam for the facility, already reduced to 400 feet from 500 during the design process, will be further shortened, they said.

Halting work on the science experiments that were to have been attached to the station's exterior will eliminate about 240 jobs, Lenoir said. Those projects are managed by Goddard Space Flight Center in Greenbelt, but many of the jobs are with contractors elsewhere.