An unhappy Senate Armed Services Committee is moving to cut the size of the Army by about two divisions -- 25,000 men -- because it thinks the all-volunteer service is now having to fill its ranks with unqualified men.

The committee is expected to recommend the retrenchment today as part of the military procurement bill on which it is working. Its recommendation comes in a year when Congress has mostly been moving to expand the military, to meet what both Congress and the administration perceive as new Soviet and other threats abroad.

It also comes at a time of renewed debate about the quality of the all-volunteer armed forces, and whether the Pentagon should return to the draft.

The Army chief of staff, Gen. E. C. Meyer, vigorously attacked the committee proposal yesterday, saying it would create "a great degree of turbulence" and exacerbate the problems of "readiness and retention" of skilled personnel.

But Sen. Sam Nunn (D-Ga.), who is championing the proposal, said in a separate interview that the committee, of which he is a leading member, wants to "put out a clear signal" that the Army should favor quality over quantity in the future.

He said he and other committee members think the Army's quality is deteriorating and decided something drastic had to be done. "Parents are telling their children not to go into the Army," Nunn said.

Asked if his proposal would pave the way for resumption of the draft, he said: "Just the opposite. We're saying we refuse to stand by and let the Army continue to deteriorate."

Under the program favored by Nunn, approved by his personnel subcommittee and coming before the full committee today, the Army would be reduced by 25,000 people for fiscal 1981.

The Army could get back to its desired strength of 775,800 for that year only by signing up a higher percentage of high school graduates than it is recruiting at present.

Staring from a base of 750,000 people, the Army could add 1,250 people to that total every time it increased the proportion of high school graduates recruited by 1 percent.

Currently, about 50 percent of Army enlistees are high school graduates. Critics consider this percentage too low, especially since the Marine Corps figure is 75 percent. The Army would not start earning back the proposed reduction until 52 percent of recruits are high school graduates.

Besides his personnel subcommittee, Nunn said, Chairman John C. Stennis (D-Miss.) of the full committee "is favorably disposed" to imposing the reduction on the Army.

The same committee cut the strength of the Marine Corps several years ago in hopes of improving its quality. Nunn said that this had worked and that Marine leaders ended up being grateful for the action.

But early indications from the House Armed Services Committee indicate members there would fight any such reduction if the Nunn proposal ends up in the Pentagon's procurement bill for fiscal 1981. Chairman Melvin Price (D-Ill.) of the House committee called attention to the Senate initiative yesterday, and questions about it drew opposition from both Meyer and Army Secretary Clifford L. Alexander.

"I am violently opposed to this on an emotional basis and on a professional basis," Meyer said while testifying before the House committee on the general state of the Army.

He said cutting strength at this precarious moment would send the wrong signal to the Soviet Union and the rest of the world. It would be "inexcusable" to have to admit the ranks of the American Army could not be filled, he added.

If the Army were cut by 25,000 people, which Meyer and Alexander said equalled about two divisions, the skilled people would have to be moved around more frequently than they are today to handle shortages. This, Meyer said, would result in even more noncommissioned officers -- already in short supply -- quitting the Army in protest.

In another exchange, Rep. Dan Daniel (D-Va.) told Meyer and Alexander that the Army was becoming disproportionately black and that this boded ill for the future. Daniel said no one sector of society should bear an inordinate burden in defending the country.

"The Army is 30 percent black," said Daniel, far greater than the percentage of blacks in the general population. "What's going to happen if we have another war?" Daniel said that Army leaders had an obligation to "broaden the base" so that blacks did not bear a disproportionate share of the casualties in any future war.

Secretary Alexander replied, "I don't know which volunteer we tell: 'Hold it! You don't come in.'"

Rep. Don Bailey (D-Pa.), a Vietnam war combat veteran, complained to Meyer and Alexander that "You're overstating the quality of this volunteer service and you're not doing the country a favor by doing it . . . We do have a problem."

In a separate development yesterday, the House Armed Services military compensation subcommittee approved the so-called Nunn-Warner amendment to give extra money to certain specialists in the armed services in hopes of inspiring a larger percentage of them to stay in.

Chairman Bill Nichols (D-Ala.) said that his subcommittee also had made progress on approving the package of military benefits promised by President Carter aboard the aircraft carrier Nimitz on Memorial Day. Nichols said, however, that there is no way to finance this $1 billion package of benefits in fiscal 1981 under the current congressional budget ceiling.

The Carter administration, he said, will have to send a supplemental request to Congress if it wants those benefits funded without cutting deeply into existing military accounts.