NASA's controversial plan to build a $32 billion space station received a major setback yesterday when agency engineers reported that astronauts might have to spend more than 3,200 hours a year on hazardous space walks to make repairs, a finding they said calls for a major redesign.

The report comes as confidence in the National Aeronautics and Space Administration was sagging because of costly problems with two other programs, the grounded space shuttles plagued by leaky hydrogen fuel lines and the badly flawed vision of the Hubble Space Telescope. The report also comes as budget-conscious legislators are reexamining the country's need for a space station.

In commenting on what it called the "profound implications" of its analysis, the report said, "these results significantly impact the current details of {Space Station Freedom's} design, assembly plans and operational procedures."

The report also said that during the peak year, the number of hours spent in space walks could reach 6,462, an average of 10.4 two-man space walks per week.

The report included 100 proposals for redesigning elements of the space station that the engineers said could reduce the outdoor working time to a more manageable 507 hours a year. The proposals range from standardizing the equipment on the station's exterior to redesigning equipment so that it can be repaired by robots. Under the current design, there are more than 8,000 objects on the space station's exterior, each of which can require repair or replacement. The objects range from thermal blankets and light bulbs to cameras to antennas and navigational equipment.

The report does not say how much it would cost to adopt all the recommendations.

NASA officials are concerned about time spent space walking because it takes away from the time astronauts can devote to experiments. Space walking also exposes astronauts to the hazards of radiation and impact from orbiting debris.

Since the space program began, U.S. astronauts have spent 400 hours walking in space.

The agency came up with a number of hours by studying how long it took astronauts to complete certain tasks under water, a routine simulation of working in weightlessness. They also computed in the number of potentially breakable pieces of equipment on the station's exterior, the rate at which each of those pieces was expected to break, and other factors.

"The external maintenance on the space station is substantial," said Charles Price, chief of robotics systems at the Johnson Space Station and co-chairman of NASA's External Maintenance Task Team, one of the committees that prepared the report. "A significant amount of activity is going to be required and it is driven by the scope of the space station itself."

However, the 3,200-hour estimate is only accurate "if you did nothing, which of course we're not going to do," NASA spokesman Mark Hess said.

The report's 100 recommendations for ways of reducing the amount of time astronauts spend outside also include:

Developing a plan to fix equipment that breaks during the four years it takes to build the station.

Devising ways to reduce the time needed to prepare for a space walk, which can run to several hours for every hour spent working. This might include developing high-pressure suits or lowering pressure inside the station so astronauts would have to spend less time getting ready to go outside. Like scuba divers coming up from the deep, astronauts now have to spend several hours clearing their bloodstream of nitrogen before going into space, said William Fisher, co-chairman of the team that wrote the report.

The report's recommendations will be evaluated by NASA officials and decided on by the end of the year. The first launch of equipment for the station is now scheduled for March 1995.

Also yesterday, NASA officials said a new $600,000 thruster will have to be installed on the space shuttle Discovery because one fell off a stand and was dented during routine maintenance work Thursday. The accident is not expected to delay launch of the shuttle, scheduled for October.