The National Aeronautics and Space Administration and the Pentagon have begun research on futuristic spacecraft, both manned and unmanned, but these programs will not be ready in time to fill the void in the nation's space program left by the destruction of the shuttle Challenger, congressional and administration sources said yesterday.

Among the operations plans in the shuttle program are alternatives developed out of "catastrophic scenarios" -- such as the loss of a shuttle, a former official said.

One option calls for taking some military satellites scheduled for shuttle launch and instead putting them into orbit with unmanned missile launchers now maintained by the Air Force.

The in-flight destruction of Challenger reopened an old battle between scientists who want greater attention paid to unmanned space probes and NASA officials' emphasis on manned flights such as moon-landing missions, Skylab and the shuttle.

Rep. Bill Green (R-N.Y.), a ranking minority member of the House Appropriations subcommittee that oversees NASA, endorsed the idea of more unmanned flights and said that putting humans in space costs more money than it is worth.

"I think the best estimate I've heard is that most missions could be done at one-fifth the cost if you didn't have people to worry about. From a purely scientific point of view, an instrumented, expendable launch vehicle would be better," Green said.

His view echoed those of physicists Thomas Gold of Cornell University and Fritz Rohrlich of the University of Syracuse, longtime proponents of more unmanned space probes.

"I think the whole shuttle program has been an absolute disaster for the space program," said Gold, who has been making the same argument before congressional committees, scientific groups and NASA panels for more than 20 years. The preoccupation with the shuttle forced NASA to "scrap an awful lot of space science" and cost the United States its world lead in the development of launch vehicles, he added.

"I regard it as quite imprudent to use manned flight when men are not needed. If NASA really had a good commercial shuttle service it wouldn't have to fill the spacecraft with senators, congressmen and schoolteachers for publicity reasons," said Gold.

The space agency, though, views people as a key component of the U.S. space program, fully justified by the ability of the shuttle crew to repair and rescue satellites.

Flying legislators, such as Rep. Bill Nelson (D-Fla.) and Sen. Jake Garn (R-Utah), and schoolteachers such as Christa McAuliffe, who died in the explosion of Challenger, are seen by NASA as a way to increase public enthusiasm for the space program.

The immediate decision facing the Reagan administration is how to handle the planned shuttle loads for the rest of the decade with three rather than four shuttles.

Annual shuttle flights were programmed to slowly rise from 15 to 24 by 1990. According to NASA plans, the Pentagon was to use one-third of the flights for military needs. NASA and the National Oceanic and Atmospheric Administration were to use another 40 percent for weather satellites and scientific experiments, and foreign and domestic commercial interests would use the balance, primarily for communications satellites.

Pentagon spokesman Bob Sims told reporters yesterday that destruction of Challenger "affects all users of the shuttle transportation system." Sims said it "clearly has a serious impact on defense programs . . . but at the moment we do not have a full assessment."

Six commercial satellites were scheduled to be launched on three of the 15 shuttle missions originally scheduled for this year. Three were set for June launching, with the others in September and November.

"We are going to lose a lot of commercial business," said Rep. George E. Brown Jr. (D-Calif.), a ranking member of the House Science and Technology Committee. "It's going to go to Ariane a rocket launched by a European space consortium or private companies. It will give a shot in the arm to the private launch companies."

"NASA has only one option," according to one former administration official who was involved in the space program. "It has to find out what happened, fix the three remaining shuttles and then determine if we have to build a fourth shuttle."

Using spare parts on hand, and the Rockwell International Corp. assembly line that is still open, NASA could purchase another shuttle for delivery "in about five years for about $1.7 billion," according to a congressional source.

NASA sought approval several years ago for a fifth shuttle in case one of the other four was destroyed, but was turned down by the Office of Management and Budget, according to the former official.

Another possible alternative to building another shuttle would be expansion of a $2 billion program approved by Congress last year for the Air Force to build 10 new boosters capable of putting 10,000-pound satellites in orbit. These missiles were to supplement the shuttle military cargoes by launching two large satellites each year from 1988 through 1993.

One futuristic spacecraft on the drawing boards may be used as an argument against a fourth shuttle, even though that extra shuttle has the support of some influential lawmakers.

Well before the accident, the Pentagon and NASA sought congressional approval to reprogram 1986 funds for research on an "aerospace plane" powered by a revolutionary ram-jet engine that would permit it to take off from a runway, go into orbit and return to Earth much like an ordinary airplane.

The first phase of that research, which would take roughly four years and nearly $500 million, would determine whether materials could be made to withstand the intense heat such an engine would generate, one source said. A second four-year phase, he said, would be needed to produce a prototype craft, much like the SR71 "Blackbird" spy plane, a sophisticated offspring of the old U2 spy plane.

The final version, which would not be ready until at least the mid-1990s, would be about the size of a Boeing 747 airliner and capable of carrying up to 100,000 pounds of cargo, more than twice that of the shuttle.

A yearlong Pentagon-NASA study of future launchers to carry cargo into space is due in May and is expected to recommend development of a giant, unmanned booster rocket that could put into orbit payloads six times heavier than those carried by the shuttle.

It could be ready in the early 1990s, one source said, because it is based on the shuttle launch systems.

A key factor throughout the history of the shuttle program has been the difficulty in projecting what the vehicle would carry in the future.

During congressional hearings last July, NASA and Pentagon officials traced the history of miscalculations that has marked the program.

Chester M. Lee, director of NASA's customer services, pointed out that in 1977, his organization projected 45 flights a year during the shuttle system's first three years of operation. Instead, he noted, "we have actually flown 17 flights . . . plus four test flights."

Overbooking of Defense and NASA flights, he said, prevented taking on commercial customers in the years after the first shuttle flight in 1981. Those customers consequently turned to the European rocket consortium.

Compounding that problem, he continued, was the overestimation of commercial business that would develop from the launching of privately owned communications satellites. "The facts of life," Lee said, "are that these have not come to fruition" because high demand for those facilities failed to materialize.

Military launches also have failed to live up to projections. A Pentagon witness said that the services to date used only 70 percent of the launch space they reserved because of delay in their satellites or in the availability of the shuttle.

Major shuttle users during the 1990-95 period are the proposed space station, which will require up to nine launches a year, and President Reagan's Strategic Defense Initiative, the "Star Wars" research program, which may involve up to four launches a year