The House Armed Services Committee, in the first major congressional decision on how to reduce President Reagan's defense budget, yesterday voted to freeze the size of the Army, Navy, Air Force and Marine Corps at present levels rather than add 37,300 troops Reagan had requested.

The committee, which historically has been the most supportive of Pentagon requests, decided in closed session to hold down manpower rather than eliminate expensive superweapons when forced to choose ways to keep 1984 defense spending within limits being set by the congressional budget process.

Committee sources said Republicans joined Democrats in voting overwhelmingly for the manpower freeze. A last-minute plea by supporters of the Navy to add 11,900 officers and sailors to run the new ships being built during the Reagan defense buildup also was denied by a lopsided margin, according to the sources.

While freezing active duty troop levels, the committee authorized increasing the National Guard by about 7,000 men and women. Rep. G.V. (Sonny) Montgomery (D-Miss.), a senior Armed Services Committee member and a leading advocate of the National Guard, hailed yesterday's action as "a first" and said "we wanted to send a message to the president to give more missions and equipment to the reserves."

Yesterday's vote was the first example of a forecast by Rep. Les Aspin (D-Wis.), chairman of the House committee's manpower subcommittee, that congressional politics was focusing on manpower as the principal means of holding down Reagan's proposed increase in defense spending.

The Senate Armed Services Committee has also expressed interest in this approach to reducing the real growth in Reagan's fiscal 1984 defense budget from his projected 10 percent to between 5 and 7.5 percent.

Reagan, as part of his program for rearming America, said the active duty military should grow by 37,300. The increases would have been apportioned among the services this way: Army, 2,600; Navy, 11,900; Air Force, 20,100; Marines, 2,700.

Long before yesterday's vote, the Army's leadership looked at the weapons bills to fall due in this decade and decided it could not afford to pay them and have more divisions as well. It opted for hardware instead of soldiers to carry out its biggest modernization since World War II.

The Navy, however, ran the risk of building a 600-ship Navy without having enough men to run them if it took that course.

So it has pressed Congress to buy both, a plea that its supporters repeated vehemently during the committee debate behind closed doors yesterday.

One committee member in the closed session said that what helped sink the Navy was the disclosure that of the projected 11,900 increase in officers and sailors, only 4,800 would go to ships.

The advent of the B1 bomber, MX missile and small Midgetman missile will require a big increase in Air Force manpower to operate and maintain them. The Air Force estimates, for example, that it would take 50,000 people to operate, maintain and guard a force of 1,000 Midgetmen.

The Marines' high command plans to stay small, so yesterday's vote poses the least threat to the Corps.

If Congress ends up freezing active duty forces at their current levels, the future of Reagan's rearmament program will be in doubt, particularly the 600-ship Navy and the nuclear delivery forces of the Air Force.

The services, faced with an aggregate cut of 37,300 active duty people, would have to revamp their deployment plans around the world, perhaps deciding to reduce the U.S. military presence in Europe rather than be short in forces on call for Persian Gulf emergencies.