A military career lost a lot of its appeal to America's young men between 1975 and 1976, Army leaders said yesterday in warning Congress that they were in an uphill fight to fill their ranks with volunteers.

But Army Secretary Clifford L. Alexander Jr. and Gen. Bernard W. Rogers, Army chief of staff, did not couple this warning with any request for resuming the draft. Rather, they called for stepped-up efforts to recruit high quality volunteers.

Alexander and Rogers, in the Army "posture" statement for fiscal 1978, which starts Oct. 1, cited a recent Pentagon poll as evidence that enthusiasm for a military career is declining among young men between the ages of 16 and 21.

Pentagon officials said yesterday that the poll, conducted for the Defense Department by Market Facts Inc. of Chicago, indicated that some of the list enthusiasm for the military stemmed from the fact that more civilian jobs are available.

To help determine the general attitude toward the military among males 16 to 21 years of age, the pollsters asked 5,500 of them across the country about their future plans in the fall of 1975 and in the fall of 1976.

The pollsters found that 8.9 per cent of the youths surveyed in 1975 said they were thinking of joining some branch of the military. That proportion dropped to 6.2 per cent last fall.

The pollsters also asked how the young men felt about becoming a laborer, salesman, serving in the military or working in an office. They were asked to answer "definitely, probably, probably not or definitely not" in regard to each job.

Here are the results among young men who said they would definitely or probably choose the military over the other jobs the pollster mentioned:

Alexander and Rogers said in their joint statement that "the significant decline in the disposition of young men toward enlisting in the "Army" was one reason the Army failed to attract as many high quality volunteers as it had sought in fiscal 1976.

The Army and other military services have concluded that high school graduates make the most successful recruits meaning that fewer of them drop out before their hitches expire. But the Army failed to sign up 62 per cent high school graduates in fiscal 1976, falling 6 per cent short of that goal.

The higher dropout rate from enlisting lower, quality men, the Army leaders said, will end up costing an extra $71 million over the next three years "in personnel related costs."

The higher the dropout rate, the more money that has to go into recruiting new men to fill the gaps, Alexander and Rogers said, citing what they called the "vicious cycle of higher costs for lower quality."

"Reversal of this trend is the key to the continuing success of the volunteer total Army," they said.

President Carter and Defense Secretary Harold Brown have said recently that the volunteer military seems to be working.They have no immediate plans to ask Congress to resume the draft. But Brown has asked for a new study on how to attract high quality volunteers despite the apparent decline in enthusiasm for a military career.

Ideas range from admitting more women into the military to allowing people with certain physical handicaps fill specific jobs within the service.