The Republican-controlled Senate Armed Services subcommittee on manpower has voted in secret session to cut the Pentagon payroll by 175,000 people over the next two years to help hold down defense spending, it was learned yesterday.

The cut, if enacted, would require reducing the active duty force of the Army, Navy, Air Force and Marine Corps by 75,000 service personnel and the Defense Department's civilian work force by 100,000 employes over fiscal 1986 and 1987.

At the same session, the subcommittee voted to delay President Reagan's recommended 3 percent pay raise for the military from July to January, when it would be raised to 4 percent.

The manpower subcommittee's votes were the first congressional actions dealing with the nuts and bolts of Reagan's $313.7 billion fiscal 1986 defense budget request. The Senate Budget Committee voted earlier to cut his budget by about $18.5 billion, but that action is not binding and does not deal with individual programs.

The subcommittee actions indicate that the Republican majority on the Senate Armed Services Committee has targeted manpower and distant projects such as the "Stealth" bomber to reduce the total defense budget while saving jobs tied to such active programs as the MX missile, B1 bomber and Navy shipbuilding.

Of all the actions taken by Congress so far on the new military budget, Pentagon officials are most upset about the proposed manpower cuts, especially for the active duty forces.

"It would be back to the hollow Army and new ships being delivered without enough people to run them," said one Defense Department executive, who declined to be quoted by name on grounds that the Senate subcommittee's actions officially are secret.

Republicans voted against Reagan and Democrats for him on the manpower issue in the subcommittee last Thursday, sources said.

Reagan's new defense budget calls for increasing active duty strength of 2.15 million by 27,000 and the civilian work force of slightly more than 1 million by 18,000.

If the subcommittee recommendation is followed, the active duty strength of the military would be 102,000 below the level Reagan says is vital to his rearmament program.

Sen. Warren B. Rudman (R-N.H.), who championed the manpower cuts in the subcommittee, has contended for some time that they would cut fat, not muscle. Rudman has said that the idea is to force the Pentagon to slim down military headquarters and support units, not reduce the strength of combat outfits. The Pentagon would decide how and where to make the personnel reductions.

The Joint Chiefs of Staff are expected to vigorously oppose the proposed personnel cuts. They have been warning over the last several years that the units that stand behind the men with rifles and maintain increasingly sophisticated weapons are too thin.

Manpower cuts result in immediate savings in contrast to cancellations of weapons contracts where the savings can take years. The Defense Department figures that each person on its payroll costs an average of $30,000 a year. Lopping 175,000 people from its payroll would save $5.25 billion over the two-year period.

Pentagon officials said that the Army already has frozen its total strength at 781,000 men to help free money to pay for its largest weapons-buying program since World War II and that it could not cut personnel without hurting readiness. The other services are seeking manpower increases largely to operate new weapons, including ships for the Navy and cruise missiles in Europe for the Air Force.

Sen. Barry Goldwater (R-Ariz.), the new chairman of the Armed Services Committee, has instructed subcommittees to recommend cuts that would help the full committee arrive at three budget totals for the Pentagon in fiscal 1986: zero growth, 3 percent growth and 4 percent growth, after inflation. To reach zero growth, the committee would have to cut Reagan's request by just under $20 billion.

The Senate Armed Services seapower and force projection subcommittee voted on Monday to deny the $454 million the Air Force is seeking to put its C17 cargo plane into full-scale development.

Congressional sources said the strategy of the Republican majority on the Armed Services Committee is to recommend deep enough cuts "to remain relevant" as the Budget Committee moves toward freezing the Pentagon budget and to convince Reagan that it is time to compromise on a smaller growth rate, perhaps 3 percent, for defense.