France's leftist parties fell far short of their expected gains in Sunday's parliamentary elections, leading to widespread predictions that they will fail to gain control of the government in next week's runoff election.

The two main parties of the left - the Socialists and the Communists - buried their bitter quarrels last night in an effort to present a united front for the balloting on Sunday. Nevertheless it may be difficult for the left to win because French districting is stacked against urban and working-class areas, where the left is strongest.

Although government leaders like President Valery Giscard d'Estaing and Gaullist party chief Jacques Chirac strongly advised against excessive optimist, progovernment newspapers and many independent political analysts said the left has virtually no chance to emerge victorious in the runoff.

It is generally calculated that the combined left - including smaller leftist parties - needs at least 51 percent of the vote to get a majority of National Assembly seats. But the final results of Sunday's voting showed the left got only 49.5 percent. The voting was so heavy that it was hard to see where the left might pick up additional support.

Paradoxically, the Socialists, the only one of the four major parties that gained over its showing in the last legislative elections in 1973, was seen as the big loser.

The Socialists netted 3.5 percent more of an otherwise remarkable stable electorate. But it was half the gain they had been generally concerned and not enough either to bend their difficult Communist allies to their will or to guarantees a victory for the left in the runoffs.

Final returns from the turnout of 29 million voters, 83 percent of those eligible, give the left slightly less than an absolute majority with 49.5 percent, and the government parties 48.4 percent. The Socialists got 22.5 percent, the Communists 20.6 percent, Radicals of the Left 2.1 percent and other leftists, not formally in the alliance, 4.4 percent.

The Gaullists got 22.6 percent, the Giscardist-centrist organization 21.5 percent, and other progovernment groups 1.9 percent. The environmentalist movement got a marginal 2.1 percent, less than in recent local elections.

The official statistics put the Gaullists ahead of the Socialists by 1,320 votes.

The left, should it win, proposes to raise the minimum wage from about $350 a month to $500 immediately. The government says such a rapid increase - that would also correspondingly raise other salaries - would create runaway inflation. The left also proposes to nationalize nine of the country's leading industrial companies and all private banks. It has pledged a number of social measures, such as lowering retirement age to 60 for men and 55 for women, 40-hour week and large increases in monthly money grants to families.

The leftist agreement yesterday provides that the parties will withdraw their weaker candidates in the [WORD ILLEGIBLE] in favor of the front-running leftist candidates and actively campaign together. It was made possible by the unexpectedly consiliatory attitude of Communist leader Georges Marchais during a three-hour summit meeting at Socialist Party headquarters.

By all accounts, Marchais conceded to Socialist leader Francois Mitterrand on every issue. Early in the day, Mitterrand had reiterated his consistent position that mutual withdrawals for front-running candidates should be automatic and were "not negotiable." During the campaign Marchais had dismissed that view as "old-fashioned." He started yesterday's meeting by saying that withdrawals indeed were "not negotiable" and he hoped Mitterrand had not changed his mind about that.

A joint declaration by the Socialists, Communist and radicals of the Left concluded, "Not a single vote should be lost by the left. Everything should be done everywhere to defeat the right."

The Communists confined themselves at the summit to obtaining a commitment from their partners that the points over which the left had quarreled and broken up when its leader last met in September would be negotiated after the runoff.

Mitterrand earlier had accused the Communists of being responsibble for the thinness of the left's electoral lead because their "polemics" had blunted the leftist push toward victory.

Later, he said , however, that the agreement should create a "new dynamism." It seems likely, in any case, that it will substantially reduce the number of Socialist voters who would have refused to transfer their votes in the runoffs to front-running Communist candidates.

The leftist agreement simply recalled in broad strokes the main lines of the joint leftist government program agreed to in 1972, leaving asided such contentious issues as whether the subsidiaries of companies to be nationalized would be also be nationalized. That was argument over which the talks foundered in September, with the Socialists saying that they never meant for subsidiaries to be nationalized.

Socialist participants in yesterday's meeting said that Marchais did not even raise issues, nor did he asks for a discussion of who would get what Cabinet posts should the left win, except to ask that there be no discrimination against Communists heading any particular ministry.

The tone of a statement by Marchais Sunday night after the basic pattern of the voting returns became clear was so harsh that most independent observers and many top Socialists concluded that the Socialists to surrender to Communist demand. The only way for there to be an agreement was for

But now that the Communists have emerged from the first round of voting with most equal strength to the Socialists, the two parties' roles are virtually reversed. Before the elections, the Socialist Party appeared to be markedly stronger, and analysts agreed that it had every interest in coming to power with the Communists reduced to a junior partnership.

Since the Communists can now claim almost half the Cabinet posts by virtue of their proportion of the leftist vote, they may be the ones who would like to come to power with a Socialist Party over which they have increased leverage.

Socialist sources said before the leftist summit that the dominant mood of the party leadership was that the left has almost certainly lost and that there is therefore no point in ceding to Communist demands.

"If we crawl in front of the Communists now," said one Socialist, "we will have lost all the moral capital we have accumulated in the past six months by standing up them. We still came out the biggest party on the left. We can maintain our honor and come back for another election."

The Socialists and their allies, the Radicals of the Left, are in the lead inside the left in 300 districts and the Communists in 169. But the Communists tend to lead in districts that are more solid for the left than the Socialists in the race for the 491 National Assembly seats.

The Guallists and the centrist-Giscardist organization have already agreed to withdraw for each other's front-runners. The Gaullists leads in 265 districts and the centrists in 206.

On the right, the big winner appears to be Giscard d'Estaing. His followers won almost as many votes as the Gaullists, whose leader, Jacques Chirac, was constantly sniping at the alleged softness of the president's tactics.

Conservative opinion greeted the results as a triumph for the government. In a wild trading session that had to be extended an extra half hour, stocks on the paris exchange jumped up 9 percent in value - a record for a single day.

The franc rose 2.5 to 3.5 percent in value and the gold Napoleon coin, the favorite form of gold boarding by anxious Frenchmen, dropped 10 percent.

"The left is no longer a minority," wrote Le Monde's editor-in-chief Jacques Fauvet, "but it is not really a majority either."

Less ambiguously, his paper banner-headlined, "The left's breakthrough on the first round appears insufficient to guarantee a change of majorities on March 19."

The results of Sunday's voting seem bound to bring sighs of relief in the West German and Italian governments. Although they were relatively discreet, the Germans made clear their anxiety over having a country with Communist ministers as a neighbor.

In Italy, it was widely thought that the Communists were waiting for a leftist victory in France to argue that there was no longer any reason to exclude Communists from the Italian Cabinet.

U.S. officials said they had strict orders to avoid saying anything that could be interpreted as an attempt to organize resistance to the rise of the French left.One officials said the Carter administration was haunted by the fear of being accused of acting against a democratically elected government, as tha Nixon administration did in Chile.

Several Gaullist strategist have expressed personal astonishment that the left did not do better. Government spokesmenare attributing the reversal of the fortunes to Giscard's relatively tough last-minute appeal to the voters.