Presidents Reagan and Francois Mitterrand ended 2 1/2 hours of "candid" talks yesterday with expressions of satisfaction about U.S.-French ties but no resolution of outstanding differences on Central America, the Soviet gas pipeline and other major issues.

Speaking to reporters following the White House meeting, Mitterrand maintained that he and Reagan had succeeded in moving toward agreement on contentious questions. But the French president made no claim that the gaps had been closed, and his description of several key problems contrasted sharply with official views here.

The main purpose of his unusual one-day round trip across the Atlantic, according to Mitterrand, was to improve prospects of the seven-nation summit meeting of economically advanced nations scheduled in Versailles nearly three months from now.

As host for the summit, Mitterrand is making extensive efforts in a series of whirlwind trips to coordinate with the other leaders.

Reagan, in a ceremonial sendoff outside the White House, called the economic part of the discussions with Mitterrand "frank and productive" but added that "it would be impossible to resolve our economic differences in one day."

Mitterrand said later that they had discussed high interest rates, adverse exchange rates and other economic woes, and he expressed hope for improvements in this field by the time of the June summit.

Regarding Central America, Mitterrand spoke publicly to Reagan in the White House ceremony of the duty to oppose "poverty and exploitation" imposed by "bloody dictatorships" and to give additional assistance to "peoples who are rebelling against their fate."

He said nothing of "outside interference" by communist nations, the administration's most visible concern.

Speaking to reporters later, Mitterrand added, "It is obvious that our assessment of the situation is different" from that of Reagan. The focus of attention, he said, should be establishment in the region of democratic governments that can help people escape from the "massive poverty" imposed by oligarchies and dictatorships.

Mitterrand said he fears that if popular movements do not receive support from the West they will turn "somewhere else," an apparent reference to the communist nations.

France has supported the proposal of Mexican President Jose Lopez Portillo for a regional political settlement involving Cuba, Nicaragua and insurgent forces in El Salvador as well as the United States and its allies. The administration, according to Secretary of State Alexander M. Haig Jr., is studying this plan "in depth" but has displayed no sign of support.

Mitterrand told Reagan, he later explained, that "I feel closer to Lopez Portillo's position than to the position of anyone else."

There is "a very sharp contrast," he said, in the two nations' positions on the recent $18 million French arms sale to Nicaragua, whose military buildup has been condemned by the United States. Mitterrand said he is trying to put France in position to "move toward conciliation" rather than to complicate settlements in the area.

Haig, speaking to reporters at the State Department, said the U.S. side came away from discussions "reassured" about the nature and future of the French arms supply to Nicaragua. He did not elaborate.

On the matter of economic relations with the Soviet Union, Mitterrand made it clear he has no intention of reconsidering French participation in the $10 billion project to bring Soviet natural gas to Western Europe, despite U.S. objections and opposition.

Because the Soviet gas will be exchanged for French francs, rather than U.S. dollars as on the international oil market, the deal will provide a chance to "get out of the grip of the high dollar," Mitterrand declared with satisfaction.

On the other hand, Mitterrand said there is considerable harmony in U.S.-French views on the supply of future economic credits to the Soviet Union and suggested the possibility of overlapping views on the supply of strategic materials to the Soviets. "We will be honest allies," he said.

Mitterrand was not completely happy with the state of the Western alliance, expressing doubt at one point about whether the alliance is really alive and saying, "Everything seems to be going in all directions at all times."

The French president flew yesterday morning from Paris on a regular commercial flight of the supersonic Concorde in 3 hours, 55 minutes, arriving in New York shortly before 9 a.m. He then flew to Andrews Air Force Base via Concorde and by helicopter to the White House, arriving at 11:15 a.m.

After the meeting and a working luncheon with Reagan, Mitterrand visited the Smithsonian's Hirshhorn Museum and Sculpture Garden, submitted to interviews with French television and met print reporters. He left Washington shortly after 7 p.m. on the return flight to Paris in the sleeping compartment of a slower American-made jet.