France announced tightened controls today on foreigners here following a car-bomb explosion outside an anti-Syrian newspaper in the center of Paris yesterday.

Interior Minister Gaston Defferre told French television that the Socialist-led government will honor France's tradition of granting asylum to political refugees. But after what he described as a "small council of war" under President Francois Mitterrand, Defferre said henceforth political refugees must observe "strict neutrality" and avoid political activities or face "eventual expulsion."

Defferre appeared to be putting a strict reading on the right of political asylum in marked contrast to Socialists' previous accommodation of political refugees and foreign opposition groups headquartered here.

The measures tightening border controls and visa applications apply to resident aliens as well as entering foreigners. The action followed the expulsion of two Syrian diplomats in the wake of the bombing yesterday--which killed one person and wounded 62 others. Twelve were still hospitalized today.

Since winning office last year, the Socialists had prided themselves on turning Paris into a center for liberation movements and oppressed opposition parties from all over the world. A law last October stipulated that any foreign political movement could open offices simply by notifying the Interior Ministry.

However, France's right-wing opposition has hammered away at the Socialists about law and order with increasing effectiveness. Last week, Defferre sought to strengthen the powers of the police despite opposition from liberal Justice Minister Robert Badinter, who has sought to soften France's harsh penal code.

As a result of the Socialists' reception of opposition groups, Iranian exiles alone have more than a dozen rival organizations based in Paris.

The opposition has demanded a government crackdown on various liberation and foreign opposition groups suspected of involvement in recent terrorist operations. Defferre--in his capacity as acting prime minister in the absence of Pierre Mauroy, who is in Canada--pledged there would be daily meetings to show that the government "intends to do all in its power to stop international terrorism on our territory."

Meanwhile, the newspaper Le Monde reported that French counterespionage had been alerted for the past two weeks because of information that "Syrian hit squads" were preparing to carry out operations in France. The pro-Iraqi newspaper Al Watan Al Arabi, where the car bomb exploded yesterday, was reportedly among the potential targets provided protection by the police.

The popular afternoon newspaper France Soir gave front-page coverage to an alleged letter from Carlos, the shadowy international terrorist, threatening to blow up trains unless France freed two of his operatives who were sentenced yesterday to jail terms for illegal possession of firearms.

However, a spokesman for the nationalized railways said the letter, signed by "the friends of Carlos," was one of 81 apparently sent by practical jokers since a still-unsolved bomb explosion March 29 aboard a Paris-Toulouse train killing five passengers and wounding 27.

While the letters seemed phony, heightened police patrols in railway stations did uncover two packages of detonators and 45 sticks of explosives in luggage lockers.