Astronauts and midlevel engineers at NASA are concerned that the agency's planned $8 billion permanent space station is poorly designed and too ambitious, according to the magazine Aviation Week.

The magazine said it had obtained an internal NASA briefing document prepared by veteran astronaut Gordon Fullerton expressing the concerns. "NASA has been criticized severely recently for letting program objectives override good judgment -- is it happening again?" asked the June 20 briefing paper that the magazine said represented the views of Fullerton as well as some of his coworkers.

Space station "program morale is poor," and "people do not 'believe' in this station," the document said. "There is great concern that NASA is misrepresenting what we can do, to the Congress and the public."

These concerns have intensified space agency efforts already underway to design a smaller, simpler space station, Aviation Week and Space Technology reports in an article to be published Monday.

After news of the astronaut document, which was prepared for a briefing of NASA officials, was released by the magazine yesterday, NASA made it public.

"The station is still in a preliminary period," said NASA space station spokesman Mark Hess when asked about the document. "This is one of the things we encourage people to do -- to come to us with their concerns . . . . To say there will be changes in the station design at this point is like saying the sun will rise. It's inevitable."

The magazine says the document has "drawn broad agreement," but it also quotes Fullerton as saying he may have overstated his subjective concerns for "shock effect" in the briefing paper.

In May, NASA unveiled a new, scaled-back blueprint for a facility as long and wide as a football field, to be assembled in orbit with additional sections to be added by Japan, Europe and Canada, who are partners in the station.

But concerns about limited space shuttle launch capacity in the wake of the Challenger accident and about the ability of astronauts to assemble and service such a complex structure have forced NASA to consider an even more modest design, the magazine said.

The revised plans would allow more of the station to be assembled on the ground.

Expendable boosters will be required to supplement the shuttle in building the station, the magazine says, and NASA has initiated study of a large new unmanned booster as a result.

The briefing document expressed concerns about several technical aspects of the station design, including poor access for maintenance and the lack of a crew escape vehicle other than the shuttle.

The station faces a severe budget cut next week by the House Science and Technology space subcommittee, the magazine said.

A subcommittee source commenting on the article said members are wondering whether the program is prepared to spend money "to the tune of $410 million next year," a reference to the amount NASA has requested for the station for fiscal 1987.

He added, "There's a lot of support for the space station among committee members . Nobody wants anything we do to be taken as a sign of nonsupport, or waivering support, for the space station."

Hess said the budget cut would delay contractor competition for the right to start "cutting metal" and developing the station. President Reagan has directed a start by next year, with the target date for completion in the mid-1990s.

Also yesterday, in an apparent response to a letter from 258 members of Congress, NASA announced it will open a new door to a possible second source for shuttle booster rockets. The boosters, which caused Jan. 28 Challenger disaster, are now made only by Morton Thiokol Inc., in Utah.

The new second-source plan replaces one that lawmakers complained gave competitive advantages to Morton Thiokol.