The nomination of former ambassador Jack Hood Vaughn to be assistant administrator of the Agency for International Development is being held up in the Senate because Vaughn was once president of the Planned Parenthood Federation of America.

Sen. Jesse A. Helms (R-N.C.), who has managed to stall the appointment since June, has called Vaughn one of the "world's leading abortionists" because from 1975 to 1977 he headed the family planning group "and as such was one of the nation's leading spokesman for the expanison of abortion services."

Vaughan's is the first presidential nomination to be held up by pressure from anti-abortion groups, which are aggressively carrying their fight into new and unexpected avenues.

"Lifeletter," a publication of the Ad Hoc Committee in Defense of Life, predicted last week that the Vaughan nomination will be "the toughest abortion vote of the year," especially for senators up for reelection.

Vaughn, 60, has had a distinguished career in government, including stints as assistant secretary of state for inter-American affairs, U.S. coordinator of the Alliance for Progress, Peace Corps directior and ambassador to Colombia and Panama.

AID Administrator Douglas Bennett called it "a terrible mistake to hold up a nomination on the basis of a totally irrelevant issue." Vaughn would be in charge of Latin American and Caribbean programs at the agency.

At a hearing before the Senate Foreign Relations Committee, Helms said Vaughn's nomination is opposed by the Episcopal Latino Americano, a group of Latin American Roman Catholic bishops. AID contributes $13 million a year to the International Planned Parenthood Federation for family-planning activities in developing countries.

One of Helms' principal arguments against the Vaughn appointment was that in May the president of the anti-abortion group American Citizens Concerned for Life was denied appointment as a consultant to the old department of Health, Education and Welfare's adolescent pregnancy programs. d

Helms quoted from a letter by Surgeon General Julius B. Richmond saying "It appeared to be inappropriate to consider, for this type of position, the leader of any national organization which strongly advocated a particular position on abortion."

On a vote of 7 to 5 the committee approved Vaughn's nomination Aug. 21. Helms is expected to oppose it on the floor of the Senate, however, and could get as many as 45 votes against it, an aide predicted. The controversy could delay the matter past the election, he said.

"It befuddles me," Vaughn said in an interview Friday. "In all my years in family planning, I've never met anybody who was pro-abortion per se. The whole drive of family planning has been to provide adequate, safe facilities, and to say that abortion should be the choice of the individual woman and her doctor."

Vaughn said there are an estimated 5 million illegal abortions in Latin America each year.