The Reagan administration's chief spokesman for the Strategic Defense Initiative yesterday strongly defended the Pentagon's proposed 150 percent increase in research funds for the controversial "Star Wars" program next year, arguing that cutbacks would retard development of a broad range of new defense technologies.

Lt. Gen. James A. Abrahamson, SDI program director, told a skeptical House subcommittee that the full $3.7 billion budget request is needed to maintain "the great deal of progress" already achieved in the space-defense research program.

Speaking before a Senate subcommittee, however, former defense secretary James R. Schlesinger questioned the need for such a large funding increase, saying that few research programs can "profitably expand" faster than 35 percent yearly unless they are "reaching out to the fringes."

Schlesinger, fueling sentiment in Congress for at least a $1 billion cut in Star Wars, said the administration's request contains "some substantial cut insurance" and that $1.5 billion to $2 billion is "ample."

"The administration expects to see some reductions and they are prepared to deal with that by requesting a generous amount at the outset," said Schlesinger, who was defense secretary in 1973-75.

Abrahamson, in turn, said his office will easily absorb the $1.4 billion appropriated this fiscal year and can spend the additional funds requested for fiscal 1986 to speed development of technologies applicable both to the space-based missile defense system and to other strategic programs.

He said various components of the Star Wars system "were widely recognized to have great potential" for the development of other weapons, including sensors, which are used to detect and track missiles.

More than a third of the $3.7 billion request is earmarked for accelerated research on sensors, almost tripling last year's expenditure.

Abrahamson also defended the planned $26 billion cost of the Star Wars research program over five years, saying the Defense Department and Department of Energy were set to request $15 billion to $18 billion for similar research programs even before the administration's new focus on the space-based defense system.

One indication of opposition to the sharp budget increase within the House Armed Services subcommittee on research and development came from Rep. William L. Dickinson (R-Ala.), who questioned the need for more "think tanks" and "Beltway bandits" in the research business.

Sen. Gary Hart (D-Colo.), raising similar concerns at the Schlesinger hearing, said, "What we're seeing is the classic creation of economic and political constituencies for a vast array of programs that once unleashed will be virtually impossible to shut down."

Schlesinger objected to statements by administration officials that a Star Wars defense is a logical replacement for the current concept of deterrence, which, the administration says, is immoral because it is based on the capability of both superpowers to wipe out each other's civilian populations in a nuclear exchange.

Schlesinger said deterrence has become more sophisticated and is now based on the capability of the superpowers to knock out each other's nuclear forces. Citing moral arguments against deterrence, he said, is "reckless and pernicious. Until the end of our children's lifetime at the earliest, our security will continue to depend on deterrence, and for members of the administration to join the attack on deterrence as immoral strikes me as quite irresponsible."