The report of the Challenger commission will prompt major changes by the National Aeronautics and Space Administration that are likely to cause further delays in shuttle launches, an indefinite postponement of the "citizens in space" program and an expensive redesign of shuttle hardware, according to agency officials, members of Congress and outside space experts.

The report's sweeping recommendations, which extend beyond the technical causes of the accident, also will prompt a fundamental reassessment of the space program's goals, from NASA's planned exclusive reliance on the shuttle for satellite launches to its commitment to build an $8 billion manned space station by the mid-1990s, these officials said.

Declaring that "the whole agency needs a major reexamination," NASA Administrator James C. Fletcher yesterday took a new and more conciliatory stand toward agency critics, while promising "to regain our honor in its fullness."

Fletcher pledged to adopt most of the report's recommendations as part of a broad, top-to-bottom review of NASA management and procedures that will tighten control over major space flight centers and "will not sacrifice safety concerns to budget limitations."

"The accident was clearly caused by a series of mistakes within NASA, [agency] procedures and marginal design," Fletcher said at a news conference. "We have a very clear idea of what we need to do."

But members of Congress and outside specialists questioned whether Fletcher and NASA officials realize the full implications of the report.

Fletcher said yesterday that he still hopes to resume shuttle flights by the official target date of July 1987 -- a goal that some experts question in light of the report's recommendations.

Fletcher also said he is "optimistic" that the administration will support funds for a new $2.8 billion orbiter to replace the destroyed Challenger, despite new questions being raised by the White House.

The agency remains committed to flying a teacher, a journalist and other private citizens into space, Fletcher said, but he acknowledged that the program will be delayed until shuttle flights are deemed safe enough for them.

"As long as citizens understand the risk they are taking, then I think it's acceptable," he said. "They private citizens will not be flying on the earlier flights. We want to make sure it's as safe as we can make it before we recommence that program."

But because the report's recommendations are so far-reaching and challenge so many of the agency's fundamental assumptions about space flight, NASA will have difficulty meeting those goals while moving ahead with future space programs, some members of Congress said. For example, the report calls for major design changes, not only in the rocket booster joints that caused the accident, but in many other shuttle parts, including the orbiter's main engine, its wheels, tires and brakes, and in the crew cabin to allow for an emergency escape system.

Given current fiscal constraints, it will be almost impossible for the agency to make these fixes, buy a new orbiter and proceed on time with such longer-range goals as the space station and a new aerospace plane.

The space station -- often billed as the agency's next space spectacular -- "is only feasible if you're willing to add $1 billion to $2 billion a year for the civilian space program," said Rep. George E. Brown Jr. (D-Calif.), a member of the Science and Technology Committee. "But within the current envelope of civilian space, it's not possible . . . . You can't have a replacement shuttle, a major return to ELVs [expendable launch vehicles or unmanned rockets], a new aerospace plane and then have the space station" without delays.

The report comes at what is probably the low point in the space program. NASA has been reeling all spring not only from the Challenger disaster but from a series of other accidents that have grounded its Delta and Atlas Centaur rockets and left the country with no capability for lifting large payloads. This has forced U.S. firms to look to other countries to launch satellites.

The commission's report criticizes NASA's planned reliance on the shuttle as its exclusive launch vehicle and calls for a return to unmanned rockets. On a more fundamental level, it questions NASA's basic 1982 decision to designate the shuttle as an "operational" vehicle and calls for a slower flight rate with "rigorous controls" on cargo manifest changes that had been prompted by the agency's desire to accommodate a broad range of commercial and military customers.

The accumulated weight of this criticism, experts say, will force a rethinking of many policy debates that NASA had long assumed were settled. Should the agency continue to compete with the private sector by launching commercial payloads? Should it continue to focus on manned space flight as the centerpiece of its efforts?

"This is really the time to reconsider the entire space program," said Thomas M. Donahue, chairman of the Space Science Board of the National Academy of Sciences. "NASA is going to have to decide something that it has failed to do for the last 15 years -- and that is, what do we want the space program to accomplish?"

Donahue is among a growing number of scientific critics who contend that most of the agency's missions can be achieved through less dramatic and less expensive unmanned probes. NASA has remained committed to manned flight to retain its high visibility and win political support on Capitol Hill, many experts contend.

Fletcher yesterday made a key concession to critics. Asked if the agency still views the shuttle as a routine "operational" vehicle, he replied: "The shuttle is a research and development vehicle and, to the best of my knowledge, it will continue to be so for some years."