The planned 8 percent pay raise for military personnel would be halved in October, and the proposed 5 percent raise for civilians on the government payroll would be wiped out under the compromise budget reduction plan now on the table, Senate Armed Services Committee Chairman John G. Tower (R-Tex.) said last night.

Tower said it is "safe" to assume that President Reagan and congressional leaders intend to follow that course on military and civilian pay as they seek to drive down the government's deficit for fiscal 1983.

The plan to halve the military's promised raise dramatizes the confidence the administration feels about being able to fill the ranks of the all-voluntary military. Administration leaders also are optimistic about retaining larger numbers of highly skilled service personnel.

For lack of jobs in the civilian market, young people are lining up at recruiting stations to join the Army, Navy, Air Force and Marine Corps.

The same recession motivating them to enlist is credited by many Pentagon manpower specialists with helping to deter experienced service personnel from quitting the military.

Tower, among those in Congress who pushed military pay raises at this time last year, said last night that he favors limiting the October pay raise to 4 percent instead of the 8 percent recommended by Reagan in his original fiscal 1983 defense budget. Tower said he is assuming that civilian government workers will receive no raise.

However, there is no guarantee that the White House and Tower will prevail on such a pay package. Other ideas being discussed in Congress are civilian and military pay raises of 2 and 4 percent, respectively, or 4 percent for each. Fierce lobbying is expected on the issue.

While reducing military and civilian raises would reduce looming deficits, the administration and Congress are moving along a separate track to find ways to cut Pentagon spending by $5 billion in fiscal 1983. Whatever savings are made from reducing pay raises will not be counted against this $5 billion goal.

Instead, the current drive focuses on ways to buy fewer weapons, reduce the size of military forces and forgo building new barracks and runways at military bases.

As a major part of that effort, the Armed Services Committee recently reduced Reagan's fiscal 1983 request for procurement from $183.45 billion to $180.28 billion. Over Tower's initial objections, the Senate agreed last week to send the bill back to the Armed Services Committee for the further trims made yesterday.

Tower said he figured that the committee's original $3.16 billion cut would save $1.1 billion in spending in fiscal 1983. Procurement money approved in one year is spent over several years, so savings are not immediate. Tower said the committee found another $3.1 billion to delete yesterday, which he predicted would translate into saving $1.4 billion in actual spending.

In arriving at the $3.1 billion in budget authority cuts yesterday, the committee voted to retire 13 Sherman-class destroyers from the Navy's active duty fleet. The administration had recommended retiring 22 ships, including five used for transporting marines to world trouble spots and four guided-missile destroyers newer than the Sherman class.

The committee also said it would take about 800 Army personnel off the payroll by deactivating an unidentified battalion. The administration had recommended personnel reductions equivalent to four battalions, Tower said.

Tower said the committee also restructured the Trident submarine program. Instead of buying equipment for the older C4 submarine missile, Tower said, the committee recommends equipping the Trident from the outset with the newer D5 missile. The administration had recommended retiring an Air Force fighter-interceptor wing, Tower said, but the committee refused to agree