The space agency's request for a new, $2.8 billion shuttle orbiter ran into unexpected resistance yesterday as White House chief of staff Donald T. Regan questioned whether the administration should spend more on existing technology or seek a new generation of space vehicles, administration sources said.

During a meeting with President Reagan and top national security advisers marked by what one official called "heated debate," Regan repeatedly asked pointed questions about the need for a new shuttle orbiter, suggesting that it might be outdated by the next decade.

The administration officials said the president was told that there is "great uncertainty" about the future demands for launching civilian and military satellites and about the frequency of shuttle flights in the wake of the Jan. 28 Challenger disaster. Reagan made no decision at yesterday's meeting, officials said.

"Basically, the president asked for more information [on] whether to build another orbiter, how many expendable launch vehicles to build over what period of time and what the budgetary impact would be," said presidential spokesman Larry Speakes.

Sources said the president was given presentations yesterday by the Office of Management and Budget, the Defense Department and the National Aeronautics and Space Administration on the need for a shuttle orbiter to replace Challenger and for new unmanned rockets to carry civilian and military satellites.

Despite strong opposition from NASA, the sources said there appeared to be a consensus at the meeting behind a recommendation to shift commercial and foreign satellites off the shuttle because of a growing backlog in government payloads and a desire to spur development of a private rocket industry. If adopted as policy, this would represent a major retreat from the administration's earlier goal to make the shuttle program finance itself by launching commercial satellites for a fee.

The sources said the cost of remedying shuttle defects, as well as purchasing a new shuttle and new unmanned rockets, has been estimated by administration officials at $5 billion to $8 billion, depending on schedule factors.

The sizable cost has compounded the problem for the administration in light of the Gramm-Rudman-Hollings balanced-budget law.

One participant in the meeting, reflecting this concern, said, "Here's the first big temptation to say we didn't really mean it. If you make an exception to the rules for this, you open up the floodgates."

The sources said Regan's concerns went beyond costs to the question of whether the shuttle technology would be outdated by the time a new orbiter began flights in the next decade. One official quoted Regan as saying, "Should we be buying the technology of the '70s for use in the '90s?"

Yesterday's meeting was the first time that the president has been directly presented with the results of a contentious internal administration review of the future of the space program after Challenger. While the president has vowed to continue the program, Regan's remarks were the first indication that the White House may not support the development of an orbiter to replace Challenger.

The sources did not specify what type of advanced technology Regan was considering when he questioned the need for a fourth shuttle. However, NASA recently awarded initial contracts for a space plane dubbed the "Orient Express" that would include technology more advanced than the shuttle, which was designed in the early 1970s.

There was also discussion yesterday about a proposal for a privately financed shuttle orbiter, but some officials were skeptical that industry could raise the capital.

Another participant in yesterday's meeting said, "The people making the presentations thought that everybody had already made up their minds" to go ahead with a fourth orbiter. "There were a lot of major assumptions made that were just not correct."

This participant said Regan was not so much opposing a fourth orbiter as saying that "we don't have enough information to make any of these decisions. Come back with a lot more information."

The fourth orbiter is considered by NASA to be vital to its long-range plans to construct an $8 billion manned space station by 1994 that would serve as a scientific laboratory and ultimately a launch platform for missions into the solar system.

Also yesterday, the Senate Appropriations Committee tentatively approved spending $526 million to fix problems stemming from the Challenger disaster, but this money would not include any funds for a fourth orbiter.