In a massive show of French support for the beleaguered Polish Solidarity workers movement, tens of thousands of Parisians marched through the Left Bank here this evening in a peaceful, but emphatic, protest against yesterday's military crackdown in Poland.

Marching 50 abreast under waving French tricolors and red and white Polish flags, the demonstrators snaked through the streets for more than three hours to chants of "Free Solidarity," converging finally in the vicinity of the Polish Embassy, surrounded by riot police, just off the Invalides Esplanade on the left bank of the River Seine.

The police department, which had massed hundreds of helmeted riot police with tear gas grenades in the area, refused to estimate the protesters' numbers. Observers at the scene, however, gave estimates ranging as high as 50,000. The march was the largest of more than 24 held around France today.

The Associated Press reported that smaller demonstrations were held in Milan, West Berlin, Madrid, Copenhagen, Vienna and The Hague.

Organized by France's five major noncommunist union federations, and backed by the ruling Socialist Party of President Francois Mitterrand as well as a wide spectrum of other French political parties, the march hailing the Polish workers movement was marked by the absence of Communist red flags. The French Communist Party had refused to join the protests, calling them "irresponsible."

The Communist decision to boycott the demonstrations was echoed in a strong editorial in its official newspaper L'Humanite today blaming the Polish crisis on the "excesses" of Solidarity. The party's stand underscored its continuing political isolation, which has caused lively internal criticism of party leader Georges Marchais.

AP reported that other Western European Communist parties criticized the declaration of martial law in Poland. The Spanish Communist Party described events in Poland as a "military coup." Italy's Communist Party, the largest in Western Europe, expressed its disapproval Sunday.

The Communists' internal strains were also reflected by Premier Pierre Mauroy, who today emphasized that "the whole government" stood behind his declaration yesterday deploring the Polish military crackdown, which he termed an "interruption of Poland's democratic evolution" that could have "very serious repercussions."

Mauroy's remarks seemed to link the four Communist Cabinet members serving in his Socialist government with his party's opposition to the actions of the Polish government. Significantly, his statement today was made only after he had consulted with Charles Fiterman, his minister of state for transport and the French Communist Party's former second-in-command.

The French premier, who emphasized that there was "no difference of opinion" among his Cabinet members over the government's stand, also declared himself in favor of today's demonstrations "with all my heart."

The unpopularity of Communist leader Marchais' stand was echoed in some of the chants by tonight's demonstrators, among whom were a number of Communists defying their party leadership and wearing party buttons in their lapels to make their point.

"Give us back Walesa," groups of demonstrators chanted in reference to Solidarity leader Lech Walesa as they passed the Polish Embassy, "We will give you Marchais."