Francois Mitterrand, leader of the leftist opposition forces bidding for power in France, has canceled plans to visit the United States this year after receiving indications that he would not be able to meet President Carter, French sources reported today.

Carter's failure to agree in advance to meet with Mitterrand in Washington later this month is likely to be considered here as a boost for President Valery Giscard d'Estaing's efforts to keep Mitterrand's Socialist Party and its ally, the French Communist Party, from winning parliamentary elections next March.

Analysts are also questioning whether it represents a signal of a toucher public stand by the Carter administration on Western European Communists and their electoral allies.

The Socialists have sought in recent months to project an image of solid and wide acceptibility in other Western capitals. They have sought to reasure moderate opinion here about American reaction and other international consequences of a leftist victory, which could lead to Communist participation in the government.

A Carter-Mitterrand meeting would have been a major plus for those efforts, and would have given new prestige to Mitterrand, the left's most likely candidate for prime minister in the event of a Socialist-Communist victory in the 1978 elections.

Public opinion polls show that the Socialists and Communists would win about 54 per cent of the vote and a msjority in the National Assembly if the vote were held today. Giscard, whose seven-year term extends until 1981, would then come under tremendous pressure to choose a Socialist as his prime minister.

The latest national polls, released yesterday, showed Mitterrand continuing to be the most popular party leader in France today. His 68 per cent favorable rating is topped only by Minister of Health Simone Veil, who has a 72 per cent favorable figure.

Giscard, who as president takes a position of being above party politics, and his prime minister, Raymond Barre, were not ranked in the poll. Gaullist leader Jacques Chirac had a 49 per cent favorable rating, while Communist George Marchais was rated at 44 per cent.

Senior Socialist Party officials visited Washington this spring to sound out the Carter administration on a meeting with the President or at least a chat with Vice President Mondale in which Carter might participate at the end.

They had been encouraged by the 1976 presidential campaign, in which Carter and some of his foreign policy advisers indicated that they were not as rigidly opposed to leftist moves toward power through democratic elections in Western Europe as was then-Secretary of State Henry A. Kissinger.

Moreover, the strong possiblity that the left may win the 1978 election here has led some American officials to argue that the Carter administration should not take an attitude that would be interpreted as hostile by the Socialists.

Mitterrand, who met with Kissinger in Washington in 1975, appeared to have strong hopes of another trip, built around invitations to speak to academic and foreign policy groups, that would result in a protocol success to reflect his position as a potential prime minister.

The Carter administration has been careful not to flatly reject a meeting with Mitterrand, but there has been no response to strong Socialist suggestions that Mitterrand would be able to see Carter during a July visit. That visit has been canceled as a result.

A trip in the fall would follow Carter's meeting with Prime Minister Barre, who visits Washington in September. It would also run close to the French election campaign and it would be even more difficult leader then, Mitterrand reportedly believes. He has therefore decided against any trip at all in the absence of a clear invitation from Carter.

Government officials emphasize that Giscard has carefully abstained from making any suggestions or requests to Carter on the Mitterrand visit.

But the two presidents appear to have established a good personal relationship as a result of their meeting at the May economic summit in London and Socialist hopes for a White House visit for Mitterrand have been shrinking since them.

The Carter administration also appears to be trying to refine its position toward leftist groups in Western Europe, especially the "Eurocommunist" Parties in Italy, France and Spain. These parties assert that they are committed to democratic practicts and fair elections and that they are independent of Moscow.

The State Department stressed last month the similarity between its views on Eurocommunism and those of Kissinger. During his election campaign Carter sought to underline the contrasts.