The new director of the Peace Corps yesterday assailed a "new wave of isolationism" during a visit to Boston and said the nation must "take part in improving the world's welfare."

Donald K. Hess, who assumed the office last month, said in a press conference that more Peace Corps volunteers are needed, "especially people outside the college campuses."

"Colleges are usually a prime source for Peace Corps candidates, but recruitment must be opened up to the whole community," he said. "American businessmen and professionals are especially needed to aid the developing countries. We must be able to provide a variety of skills for a variety of problems."

Hess attributed a recent decline in the numbers of Peace Corps applicants to a "new wave of isolationism." He said the quality of service has improved with the decline, but added. "America as a whole seems to have lost interest in what we're doing.

"Understandably the aura of glamor which the Peace Corps had during the Kennedy Administration has died, since many Americans--and students in particular--are refocusing their attention to domestic problems," Hess said. "But the needs of the world are massive and continue to expand."

The reorganization last year of the Peace Corps and other government volunteer programs such as VISTA into a collective organization named ACTION compounded the problem of decreasing interest and applications. Before joining ACTION, the Corps had as many as 15,000 volunteers. Now, budget limitations have forced the Corps to cut its manpower in half.

Plans for expansion last year were suspended when Congress refused to meet the Peace Corps's request for more money. Hess said he hopes Congress will appropriate at least $88 million for the next fiscal year.

"We'll be launching an intensive recruiting effort this coming summer to look for 11,000 applicants across the nation," he said. "We'll have to expand as the size of the appropriation increases."

Responding to a reporter's suggestion that the Peace Corps may be a form of "cultural imperialism," Hess said. "I strongly hope we aren't used as an arm of U.S. foreign policy."

"For one thing, we don't serve in a country because the State Department or Administration dictates it," he said. "We serve only on the invitation of the host government. We serve on their terms and under their supervision."

Hess added that the Peace Corps, now operating in 57 countries, does not actively solicit invitations. "We have a good reputation and countries are genuinely interested in us," he said.