President Reagan's fiscal 1986 budget for NASA is seeking $7.9 billion -- just under what it would take to sustain the agency's programs at their current levels.

Just when the space program seemed poised to take off again, the budget crunch has forced the National Aeronautics and Space Administration to slow down development of the permanent space station it had hoped to put into orbit in 1992 and to delay work on any new planetary exploration missions or Earth-orbiting science projects.

NASA's request for the space station is $230 million, a figure NASA Administrator James M. Beggs acknowledged is $50 million less than the agency had sought to keep the project on schedule.

"This will force us to stretch out the next phase of development from 18 months to 21 months and start thinking about putting the station in orbit in 1993 or 1994," Beggs said. "It would have been nice to go in 1992" -- the 500th anniversary of Columbus' discovery of America -- "but we'll have to aim now for the later date."

Cutbacks by the Pentagon and other science-oriented federal agencies have also forced NASA to reduce the number of space shuttle flights planned for the next two years by a couple of missions. Beggs said the shuttle will fly 11 times this year and no more than 14 times next year.

"Our commercial flight schedule is right on target," Beggs said, "but the military flights and government-sponsored missions have decreased. The biggest swinger in our shuttle schedule is the Defense Department. That market is down considerably, almost one-third from what we had projected."

One new program covered by the budget would be development of an unmanned spacecraft, the Orbiting Maneuvering Vehicle. The craft would be carried into space in the shuttle's cargo bay, then flown by remote control up to 1,500 miles away to put satellites into higher orbit or to retrieve them. NASA is seeking $25 million to begin development of the OMV, which is expected to cost $350 million.