The expert panel that oversees safety questions for the National Aeronautics and Space Administration was aware last year of the trouble with the space shuttle's solid rocket boosters but believed that the space agency had the problem under control.

"The panel had been made aware of the erosion of the inner seal of the redundant pair [of O-rings connecting the solid rocket booster casings]," Seymour C. Himmel, a member of the NASA Aerospace Safety Advisory Panel, said yesterday.

"This was considered to be one [problem] well in hand and attended to," said Himmel, a retired NASA associate director at the Lewis Research Center near Cleveland.

Consequently, Himmel said, the problem with the O-rings -- which some observers speculate may have been responsible for the leak in the space shuttle Challenger's right-hand solid rocket booster -- was never made a part of the safety panel's formal reports.

The panel, which filed its most recent safety report prior to the Jan. 28 explosion of Challenger, expressed concern about the frequency of shuttle flights in its annual meeting yesterday with the space agency's administrator.

Describing NASA's goal of 24 shuttle launches a year as "highly ambitious," panel member John G. Stewart, said during the meeting that "the projected flight rates are not within reach at this point" and that "a more likely rate will be between 12 and 15" flights per year.

Before the Challenger accident, NASA had planned on launching 15 shuttle flights this year.

Acting NASA administrator William R. Graham did not respond directly to the statement that NASA's flight schedule should be scaled back. He told panel chairman John C. Brizendine that, "as we go into higher launch rates," NASA would seek the panel's advice on how best to assure that no safety problems would result.

NASA's view of the shuttle as a reliable means of space transport that could routinely be launched has apparently been a source of disagreement between the safety advisory panel and the NASA hierarchy.

Last year, the panel recommended that "NASA management would be well advised to avoid advertising the shuttle as being 'operational' in the airline sense when it clearly isn't. More to the point, however, is the fact that shuttle operations for the next five or 10 years are not likely to achieve the 'routine' character associated with commercial airline operations."

Responding to the panel's recommendation, NASA yesterday denied that it ever compared the shuttle to an airline operation and, in its defense, pointed to presidential directive NSDD 144, which states that "NASA's first priority is to make [the shuttle] fully operational and cost-effective in providing routine access to space."

The directive calls for a flight schedule of "up to 24 flights per year with margins for routine contingencies" built in to accommodate even more flights.

However, panel member Stewart said in an interview that "the shuttle is not, in my view, a commercially mature vehicle around which you can build a highly reliable flight vehicle."

"There is a national defense directive that was approved that became the policy document," he added. "I think NASA found themselves with a schedule to meet, and they did their damnedest to meet it."

The continuing developmental status of the shuttle raised the question of whether it is a suitable vehicle for civilian transport.

Several panel members said yesterday that issue is beyond the panel's mission. But Stewart, a Tennessee Valley Authority official, said, "We did not look into that issue and, in retrospect, we should have. It was an oversight, in my view. I think there's some serious issues to be raised in that arena."