The U.S. military attracted more high-quality people than ever during the last fiscal year, as recruitment and reenlistment improved despite an upswing in the economy, the Defense Department announced yesterday.

Lawrence J. Korb, assistant secretary of defense for manpower, reserve affairs and logistics, said that, for the first time, more than 90 percent of recruits in the Army, Navy, Air Force and Marines were high-school graduates.

During the fiscal year that ended Sept. 30, 93 percent of recruits had high-school diplomas, compared with 68 percent in fiscal 1980.

"Quite frankly, I'm astounded by the progress we've made over the last four years," he said.

Korb said the quality of young men and women entering the service is higher than during the draft years that ended in 1973. He also said the Pentagon has not had trouble attracting good people as the unemployment rate declined.

He attributed the success to pay raises and other improvements in military living conditions and to the Reagan administration's support for the armed forces.

"The people are treated well," he said. "They feel they have more prestige, and they feel that society appreciates what they do."

Even critics of the administration's military buildup, while questioning management and weapons-procurement decisions, have acknowledged an improvement in quality and morale of the volunteer force during the last four years. Some, however, have attributed that success in part to the economic recession and predicted that quality would decline as more private-sector jobs became available.

Korb said yesterday that there have been a few signs of such a dropoff. He said the number of young people waiting to enter the service at the end of fiscal 1984 was slightly smaller than at the end of fiscal 1983.

That waiting list, or deferred-entry pool, is a sign of the military's recruitment success, he said.

It includes people who want to join but must wait because the year's quotas for the service or specialty in which they are interested have been filled. There were 131,300 people on that list at the end of September, about 8,000 fewer than a year earlier.

Except for that one small indication, however, Korb said all the news is good. He said he does not believe that the economy is a major factor affecting recruitment, although he acknowledged that the unemployment rate in some areas remains high.

"All the preliminary indications tell us that, if the economy were the dominant variable, we would begin to see greater effects, and we have not seen that," Korb said.

Korb acknowledged that the active-duty force, which stands at 2,138,000 members, will have a smaller pool of 18- to 24-year-olds from which to recruit from during the coming decade because of shifting population patterns. The military had to recruit 1.8 percent of the available pool last year and will need 2.4 percent of it in fiscal 1995.

But he said he believes that the military can meet its goals without returning to a draft by continuing to keep pay competitive with private-sector salaries and by continuing to retain a larger number of personnel after their first or second tours of duty.

Last year, the four services recruited as many people as were authorized by Congress last year, 328,400. About 25 percent were minorities, compared with 23 percent in the applicable age pool, and about 12 percent were women, the Pentagon said.

The Army, which Korb said has had the most trouble attracting quality recruits, joined the other services for the first time in signing fewer than 10 percent "below-average" recruits. That means that 90 percent of the Army's recruits scored above the 30th percentile on a general-aptitude test.