The three leftist parties that hope to win control of France's National Assembly early next year acknowledged today that they reached a political deadlock threatening not only their chances in the elections but also the very existence of their alliance.

After 10 hours of progressively bitter negotiations that began yesterday morning and stretched past midnight, the leaders of the Communist, Socialist and Left Radical parties wearily broke off their efforts to reach a new joint electoral platform. They did not agree on a date or method of resuming the talks.

Each of the three parties stated through spokesman today that it was still a member of the alliance, known here as the Union of the Left, and asserted a readiness of resume talks at any time.

But angry charges of bad faith that leading Communists and Socialists exchanged in public statements today underlined a new, sharp disunity of the leftist parties that leaves France's political life in its most fragmented and stalemated state since Charles de Gaulle's rise to power ended the ineffectual Fourth Republic in 1958.

The French stock market, depressed for the past 18 months as the threat of a leftist victory at the polls seemed to grow, jumped 4 per cent in average stock values today.

Communist leader Georges Marchais warned the business community against "rejoicing too soon," predicting that the leftist parties could still get together to win the elections. But the Communists also announced that they would stage a series of mass meetings next week that are likely to be largely devoted to attacking the Socialists.

The indefinite suspension of political cooperation by the leftist parties follows a year of acrid wrangling within the coalition of Gaullists and centriests that has ruled France since 1958. President valery Giscard d'Estaing and Gaullist leader Jacques Chirac have recently lapsed into an uneasy public truce that is still marked by mutual distrust and dislike.

Giscard received another apparent electoral boost today with the announcement here that President Carter would stop in Paris for three days on his November tour of the world. Giscard has sought a Carter visit since May, when the two met in London.

The Carter administration has appeared increasingly preoccupied by the strong likelihood that a leftist victory next March would bring Communists into the government here for the first time since the end of World War II. Socialist Party leader Francois Mitterrand pledged earlier this week that this would happen if the Union of the Left does win the National Assembly elections.

While evidently not final, the widening rift between the Socialists and Communists immediately changed the French political atmosphere.

It is stimulating serious thinking within the Socialist ranks about going it alone electorally without the Communists. Some Socialist officials are already hinting publicly that the party is picking up new support from moderates because of its firm stand against the COmmunists in the platform negotiations. These officials suggest that the Socialists could form a minority government.

The negotiations have also produced a marked shift in emphasis toward militance by the French Communists, who for the past two years have sought to emphasize instead a more moderate "Eurocommunist" image of being prepared to govern with the Socialists by Western democratic methods.

In one of the more pointed barbs today, Socialist Pierre Beregovoy said his party must now ask itself if the Communists "were in the process of changing again," apparently toward a return to the party's Stalinist policies of the past.

Distrust has been growing steadily between the two leftist allies since the summer, when the Communist leadership suddenly began attacking the Socialists and demanding more binding commitments to a new version of the joint electoral platform that the three leftist parties signed in 1972.

Socialist officials say privately that the Communists took this hard line after becoming concerned over signs that the "Eurocommunist" stance was not popular with long-time party members. The Communists, for their part, have not masked their fears that the Socialists might dump them and try to govern alone if the Union of the Left wins next March.

When final negotiations by the leaders of the three parties began two weeks ago, public-opinion polls showed the Union of the Left gaining 53 per cent of the projected vote in the March balloting.

But that figure slipped to 52 per cent in polls taken immediately after the Sept. 14 adjournment of the first "summit" of leftist readers called to complete the updating of the joint platform. The first round of talks broke down when Left Radical leader Robert Fabre walked out rather than continue to discuss Communist demands that more than a thousand companies be added to the list of nine major industrial and banking groups that the 1972 platform targets for nationalization.

Throughout a weekend of hectic contact by the three-parties, the Communists scaled down the number of firms they wanted nationalized from 1,500 to 729, and the Socialists indicated that they would compromise on defense an dother issues. The talks resumed Wednesday, amid prospects that an agreement could be salvaged.

But thosehopes evaporated Thursday as the Communist refused, according to Socialist and Left Radical spokesmen to discuss any further compromise on the nationalizations.

Socialist economic spokesman Michel Rocard charged that the Communists had come into the talks already determined "to seek a break" with the Socialists rather than an agreement.

The continuing dispute is also spurring a discreet but major effort by Giscard and others in his coalition to woo Fabre's small Left Radical Party out of the leftist alliance and into the government camp, according to French political sources.

Fabre's group can claim to represent no more than to 3 to 4 per cent of the electorate, but is an important bridge for the Socialists toward the center. A defection by the Left Radicals would change the nature of the leftist coalition in the eyes of many French voters in what still promises to be an exceedingly close election, according to French political analysis.