France pledges it won't pull out of Lebanon . . . for now. But official statements suggest second thoughts

Despite grief over mounting casualties and some hints that the government may reconsider its participation in the multinational peacekeeping force, for now France intends to keep its troops in Beirut.

French officials said this was the message behind President Francois Mitterrand's surprise visit Monday to the Lebanese capital. In Beirut, the French President visited the rubble of the paratroop base and met with Lebanese President Amin Gemayel before returning home in the evening.

Back in Paris, Prime Minister Pierre Mauroy said, ''It was not yet a question'' that French troops would be withdrawn. He added that France would not give in to ''provocations.''

''France will be firm, no question about it,'' he said.

But at the same time, he said France would not increase its forces in Lebanon and its role in the fighting. France has a standing threat to take countermeasures if French forces are attacked, and the last time its soldiers were shelled, French aircraft bombed the offending batteries.

This time, however, the attack came from a suicide truck, making it hard to offer any suitable reprisal. Although many commentators suspect Iranian complicity, perhaps together with the Syrians, government officials are making no public accusations.

Except for the lack of accusations, Paris seems to be taking the same line as Washington: no withdrawal and no escalation. But Prime Minister Mauroy was not as firm as President Reagan. By refusing to state explicitly that French troops will stay there. Mr. Mauroy seemed to leave the French government's options open to review.

Foreign Minister Claude Cheysson added to the feeling the French were having second thoughts when he said, ''When we are attacked, we can ask if our military force is still necessary.''

Foreign Ministry officials attempted to play down Mr. Cheysson's statement, saying he was only evoking a hypothesis.

Nevertheless, as the Lebanese situation has deteriorated, questions are being raised about whether the French troops have become sitting ducks for no good reason.

The latest polls before the attack showed that 56 percent of the public disapproved of the sending of French troops to Lebanon. Nearly two-thirds considered that France's obligations to its former mandated territory did not warrant the loss of French lives - and even before the weekend's outrage some 17 French soldiers had died in Lebanon.

This opposition to the Lebanese engagement is bound to grow as the French death toll continues to increase. The latest count from Sunday's bombing, according to the French Defense Ministry, is 22 killed, 14 wounded, and 36 missing. Many of those still under the rubble are presumed dead.

Inside the government, the Communist Party called Sunday for immediate withdrawal. Party spokesman Guy Hermier called for a United Nations peacekeeping force to replace the present four-nation multinational force.

Defense Minister Charles Hernu has proposed this solution in the past. But it failed to make any headway, and no Socialist spokesman has brought it up again after the recent attack.

The search for a face-saving way out may be continuing behind closed doors, but so far the government is not ready publicly to reconsider its position about Lebanon. As restated Sunday evening by Prime Minister Mauroy, this position is for French troops to protect civilians in Beirut and work for ''the restoration of sovereignty and unity of Lebanon.''

Despite increased public anxiety over this role, the government should have no problem politically keeping the troops in Beirut. Under the Constitution, the President has wide discretionary powers in foreign affairs. There is no French equivalent to the War Powers Act, and no legislative influence over foreign policy.

It is hard, too, for the conservative opposition to criticize a leftist government for being resolute. So, in a curious irony, conservative leaders have been echoing Socialist government spokesmen.

''It's a necessary mission,'' said the Union Democratique Francaise's Jean Lecanuet.