Less than one-third of last June's ROTC graduates will have to serve more than six months on active duty, the Army announced last night. Over 6,000 men will be affected by this development, including some 60 Harvard graduates.

Col. Trevor N. Dupuy, professor of Military Science and Tactics, said he knew of the Army's program, and added that the same policy may hold for this June's class also.

The reason for the shortened tours, it was learned, is the smaller size of the standing Army, and an unexpected increase in the number of officers who have volunteered for extended active duty.

Dupuy said the Army has sent questionnaires to all men in the senior ROTC class, asking them whether they would prefer to serve the normal two-year active tour, or the abbreviated six-months one.

Require Extensive Reserve Duty

Those men who choose to serve only a half-year will be assigned to "active participation" with reserve units, the Army said. This means they will be required to participate in drills about once a week for 7 1/2 years.

If a man chooses to serve for two years on active duty, he would only have to participate for three years of reserve duty. It is understood, however, that last June's graduates may be able to escape the lengthy 7 1/2 year reserve requirement, since it was not put into effect until last August, two months after their graduation.

In the event that too many men request two-year duty, Distinguished Military Graduates will be given first preference, the Army said. In addition, men in the Artillery and Engineers Corps will also be given certain priorities.