Going back to the draft would reduce the quality of the Army as well as rekindle the "anti-draft sentiment," the Pentagon said yesterday in a generally favorable report on the all-volunteer military.

The report represents the Carter administration's first detailed look at the all-volunteer force that came into being in 1973 when the authority to draft young men expired.

While conceding that some problems do plague the all-volunteer force, the report said the services should be able to fill their ranks "throughout the 1980s" with high-quality volunteers.

This forecast is under increasing challenge these days, with Congress expected to consider it next year.

Rep. Robin L. Beard (R-Tenn.), a member of the House Armed Services Committee, for example, recentlysent a detailed critique of the all-volunteer force to academic leaders and asked them to join the national search for alternatives.

The Pentagon yesterday said its own 390-page report "is not intended to either defend or attack the all-volunteer force but rather lays out the quantifiable data, structures alternatives and sets a framework for the national debate that seems to be forming around the future of the all-volunteer armed forces."

While conceding that conscripting 100,000 young men instead of relying on volunteers would save about $250 million a year, the Pentagon said "the active force draft is not needed today to man our active forces" but it would be advisable to have a standby draft that could provide troops for a "protracted" war in Europe.

In a table listing the "effects" of returning to conscription, the Pentagon said this step would "reduce quality of Army and stimulate anti-draft sentiment."

The Joint Chiefs of Staff have approached the draft question gingerly, limiting themselves so far to recommending that the draft machinery be readied for use, including returning to the registration of teen-agers. They have not recommended ending the all-volunteer experiment and reinstituting draft calls.

These are some of the pluses the Pentagon said it found in its two-year study of the all-volunteer force (AVF):

The education levels and test scores of new recruits have been higher under the AVF than under the draft.

The young people who joined the military in fiscal 1978 represented "the highest percentage of high school graduates of any year in our nation's history."

The volunteers represent a geographic cross-section of the nation, although the percentage of blacks signing up is disproportionate.

Discipline problems have declined since the Vietnam era, "returning to about the pre-Vietnam level."

There are better opportunities for women and minorities, better living conditions for junior personnel and a wider choice of training.

In examining some of the minuses of switching to the AVF, the Pentagon included these on its list:

Army recruits' test scores have been declining since fiscal 1976, and Navy discipline is not keeping up with the favorable trends in the other services.

Almost 50 percent more recruits are leaving the service before finishing their obligated tours than was the case under the draft.

There is a perception that military health care is inadequate.