The Pentagon has some good news for president-elect Ronald Reagan: volunteers are filling up the ranks of the armed services.

So much so, in fact, that in the fiscal year just ended, the Army, Air Force and Navy signed up as many young men as they wanted, while the Marine Corps missed its quota by less than 1 percent.

Reagan said repeatedly during his campaign that he opposed returning to the draft. Instead, he favored paying military people more and improving benefits to make service careers competitive with civilian ones.

However -- there is always a however in discussing recruiting trends -- manpower specialists credit the recession with driving young men into the military. Many volunteers decided they could not find good-paying jobs in the civilian market. So, if Reagan makes good on his promise to improve the economy, military recruiters will again face an uphill road.

While recruiters did well in getting people in the front door in fiscal 1980, the large exodus of skilled military technicians continued. One decision for Reagan will be how much more money should be invested in bonuses and benefits to stem this exodus, which undercuts the military's readiness to fight.

The Carter administration has drafted bills to pay officers and sailors on surface ships and submarines $150 million in bonuses in hopes of persuading them to stay in the Navy. These proposals, to be submitted to Congress next week, come atop the 11.7 percent military pay raise enacted shortly before Congress recessed for the election.

The Pentagon's recently released statistical profile on its fiscal 1980 effort to fill the ranks of the all-volunteer force, which replaced the draft in 1973, shows these trends:

The four services signed up 389,000 men and women, 15 percent more than in fiscal 1979. Counting those who left the service and rejoined, each branch achieved 100 percent of its quota. In fiscal 1979, the Army got 89 percent of the volunteers it sought, the Navy 94 percent and the Air Force and Marine Corps 98 percent each.

In their quests for young males never before in the military, the Army achieved 101 percent of its objective, compared with 86 percent in fiscal 1979; the Navy and Air Force 100 percent, compared with 93 and 97 percent, respectively, the previous year, and the Marine Corps 99 percent, compared with 97 percent in fiscal 1979.

Women signed up for the military with such eagerness that every service except the Army, which has the most room for them, got as many female volunteers as it could use. The Army enlisted 22,200 women, or 95 percent of its quota -- a 4 percent increase over fiscal 1979.

The Army and Navy did worse at recruiting high school graduates in fiscal 1980 than in fiscal 1979. The Air Force remained the same, and the Marine Corps did better. The proportion of high school graduates among the men and women recruited in fiscal 1980 were: Army, 54 percent; Navy, 75 percent; Marine Corps, 78 percent; Air Force, 83 percent.

The services recruited slightly fewer blacks. The percentage of blacks signed up in fiscal 1980 was: Army, 30 percent; Navy, 13 percent; Air Force, 15 percent; Marine Corps, 23 percent. The fiscal 1979 percentages were: Army, 37; Navy, 16; Air Force, 16; Marine Corps, 28.