Paris — French Communists are fuming over President Francois Mitterrand's austerity program. They refuse to endorse intervention in Chad or Lebanon. And they criticize the Mitterrand government's support for deployment of American missiles in Western Europe and its insistence that France's force de frappem be kept out of the Geneva nuclear talks.
No wonder, then, that the Communists are in deep trouble with their Socialist allies, the dominant partners of the governing coalition.
The marriage has gone so sour that the Socialists have called an emergency summit meeting today.
''We have many questions to ask the Communists,'' Marcel Debarge, Socialist Party official responsible for relations with the Communists. ''The Communist Party just can't keep on criticizing.''
The problem is Communist restlessness. Communists were accused of stuffing ballot boxes in March's municipal elections in the so-called ''red belt'' of Paris suburbs. They have lost all four by-elections held so far this fall.
The setbacks mirror the decline in party popularity nationwide. The party won some 15 percent of the vote in the 1981 presidential contest, but polls now put it as low as 10 percent.
There are many reasons for the decline. More affluent French workers have lost enthusiasm for the party's Marxist policies. Fraud charges have tarnished a reputation for honesty. And support for such unpopular Soviet actions as the invasion of Afghanistan, the crackdown in Poland, and the Kremlin's position on Euromissiles has hurt.
As the Communists see it, though, the main problem is unpopular Socialist ''rigor,'' which is increasing unemployment and cutting workers' purchasing power.
''We lost primarily because people are dissatisfied with the change on the national level,'' says Pierre Thomas, a recently defeated Communist mayor. ''Promises made have not been taken.''
Mr. Thomas has a point. To regain momentum, he and his fellow Communists recently increased attacks on these economic policies. In November the Communist president of the state coal board resigned because of state subsidy cuts that could put 20,000 miners out of work.
At the same time, unions have assumed a higher profile. Strikes could follow.
Such a prospect clearly scares the Socialists. They have a majority in the National Assembly and don't need the Communists to rule.
But if the party quits the government, it could wreck havoc with a wave of strikes inspired by the Communist-dominated Confederation Generale du Travail (CGT). It could also criticize with an even stronger voice, draining support from the government's supporters on the left.
Socialist Debarge says, ''Overall it's better if they stay.''
The Communists themselves have strong reasons to remain. Their four ministries give them legitimacy - and the power to appoint Communists to positions throughout the bureaucracy. Leaving with the spotlight on their criticisms of the Euromissiles, Lebanon, and Chad would hurt politically.
So today's meeting will probably avert an outright split. But it is uncertain how long any agreement will last. Every municipal defeat makes the Communists more nervous. Every CGT strike scares the Socialists.