A House Armed Services subcommittee yesterday cut $4 billion from next year's $18.2 billion Pentagon retirement fund request, in a move to force revision of the military pension program, congressional sources said.

The panel also directed Defense Secretary Caspar W. Weinberger to develop a new pension plan for future servicemen that conforms to the lower fund level.

In adopting the plan proposed by Armed Services Committee Chairman Les Aspin (D-Wis.), the military personnel subcommittee voted to preserve present pension rates for the 2.1 million men and women now on active duty and for the 1.1 million retired military personnel.

The military pension plan, which permits individuals to retire at 50 percent of base pay for life after 20 years of service, has been increasingly criticized in recent years for encouraging early retirement and for being more generous than private programs.

As part of yesterday's action, the subcommittee asked the Defense Department to investigate ways to encourage longer military careers.

Under the Aspin program, the Pentagon would be required submit its new pension plan for future military personnel to Congress, which would have to approve it before it could go into effect.

When Aspin announced his plan early last month, a spokesman for Weinberger said changes in the program were worthy of study. The chiefs of staff of the four services, however, voiced opposition when testifying last month before the subcommittee. An aide said the new committee chairman "felt so strongly" about the plan that he not only will push it through the House, but "even may hold up the spending bill if the Senate didn't agree to it."

In other action, the subcommittee cut in half the request for 25,000 more personnel and followed the lead of the Senate Armed Services Committee in delaying until Jan. 1 the administration's proposal to raise military pay 3 percent in July.

In what one congressional source described as "a sweetener" for the retirement cutback, the panel also added almost $900 million to the manpower budget for such items as funds to relocate service personnel.

The House Armed Services subcommittee on research and development yesterday approved a staff-suggested cut of $1.2 billion in the adminstration's $3.7 billion request for President Reagan's Strategic Defense Initiative (SDI), or "Star Wars," next year, according to congressional sources.

Overall, the subcommittee cut $5.1 billion from the Pentagon's $39.3 billion research and development request. The reduction is almost three times larger than the $1.8 billion cut by the Senate Armed Services Committee last month.

Nevertheless, House sources said yesterday they expect even deeper cuts in next year's research and development budget when the defense spending bill is taken up by the full committee next week.

Two subcommittee members, Reps. Ronald V. Dellums (D-Calif.) and Rep. Nicholas Mavroules (D-Mass.), who wanted to cut SDI spending next year below the subcommittee's $2.5 billion level, withheld their amendments yesterday.

Mavroules said he will attempt to cut SDI to $1.4 billion, the same level as this year, with language prohibiting any activities in violation of the 1972 Anti-Ballistic Missile Treaty.

Dellums would eliminate all demonstration tests that might violate the treaty by cutting those programs and reducing remaining SDI research funds to about $1 billion.

Rep. James A. Courter (R-N.J.), another subcommittee member, will attempt to restore funds for the program when the measure comes up next week, according to congressional sources. He also will press for language that would leave Lt. Gen. James A. Abrahamson, the SDI director, with flexibility on how to apply fund reductions, thereby prohibiting Congress from dictating which elements of the program should be cut.