President Carter will make his first official trip aborad in early May, going to London for an economic summit conference with the leaders of six other major industrial nations, the White House announced yesterday.

The two-day trip may be expanded to include a NATO meeting, also in London, and talks with Syria's President Hafez Assad somewhere in Europe, the White House said.

Carter will hold the third televised news conference of his six-week-old administration at 10 a.m. today. The ABC, CBS and NBC networks will carry it.

The ecconomic summit, attended by Britain, West Germany, Japan, France, Italy and Canada will be Carter's first chance to display his brand of politics and persuasion outside the United States.

Carter will also make his first working trip away from Washington March 16-17. He will attend an evening town meeting in Clinton, mas., march 16, fly to Charleston, W.Va., the next morning for an early afternoon panel discussion on energy, and then fly to New York for a speech at the United Nations, the White House said.,

The President will speak to the permanent representatives of U.N. member nations in the General Assembly hall.

British Prime Minister James Callaghan will be the host for the economic summit May 7-8 at his residence, 10 Downing St. Callaghan arrives in Washington today for three days of talks with Carter that are expected to revolve around the summit. He is arriving in a Concorde, the British-French supersonic airliner.

The summit is the third of a series that began in Rambouillet, France, in November, 1975, and continued in Dporado Beach, P.R., last year. At Ramnbouillet, the first time heads of state ever got together to discuss economic issues face to face, they agreed to stimulate economic expansion, cut unemployment, and let monetary exchange rates "float", or fluctuate.

At Dorado Beach , worried about renewed inflation, the leaders agreed to slow down economic expansion. Main agenda items for the London meeting include reopening the stalled dialogue between rich and poor nations, and German and Japanese reluctance to flollow the U.S. lead in stimulating expansion in an effort to help pull the economic recovery.

Callaghan has said he also hopes to get in a discussion of Carter's vocal campaign against breaches of human rights in an effort to curb some of the Presiden't senthusiasm, which is also known to worry Chancellor Helmut Schmidt of West Germany and president Valery Giscard d'Estaing of France.

In other matters, Carter confirmed yesterday that he will nominate Pittsburgh Mayor Peter F. Flaherty, an early supporter instrumental in Carter's narrow Pennsylvania win, to be deputy attorney general. White House press Secretary Jody Powell gave a firm "no" when asked if Flaherty was a political appointment.

Carter also confirmed that he will nominate former Ohio Gov. John J. Gillingan to be administrator of the Agency for International Development, and Carol T. Foreman to be a member of the board of the Commodity Credit Corp.

Foreman, president of the Consumer Federation of America, was nominated Monday to be assistant agriculture secretary for food and consumer affairs.