France's right-wing opposition parties pledged today to relax state controls over the French economy and denationalize large sectors of industry if they regain power in nationwide legislative elections in March.

The opposition's 20-point program included a promise to repeal laws on the press and electoral process passed by the present Socialist-dominated National Assembly. But it stopped short of pledging to go back on social legislation introduced since President Francois Mitterrand came to power in May 1981 as France's first left-wing president in more than a quarter of a century.

With two months to go before the elections, the latest opinion polls suggest that the neo-Gaullist Rally for the Republic and the center-right Union for French Democracy are likely to win a comfortable overall majority in the 555-seat National Assembly, putting them in a position to form a government. But the polls also indicate a narrowing in the gap between left and right as the electoral campaign begins.

Political analysts here said that the content of the opposition program raised the prospect of an early trial of strength between a right-wing government and the left-wing president, who will have two years of his seven-year mandate left.

The stability of the French Fifth Republic, inaugurated by Charles de Gaulle in 1958, has depended until now on the ability of a president to impose his will on the assembly.

Signing the program on behalf of the neo-Gaullists, former prime minister Jacques Chirac said that France needed a government that would begin swiftly the work of putting the country back on its feet. He is considered a likely prime minister in the event of a convincing right-wing victory.

The opposition platform was denounced by Prime Minister Laurent Fabius as an "attempt to demolish" everything the left-wing government had accomplished. Socialist Party Secretary Lionel Jospin predicted that it would penalize the poor, cause havoc in industry and boost inflation, which was brought down to below 5 percent last year.

While much of the program is vaguely worded -- "promote a society of freedom," reads point number one -- it also includes such detailed promises as the abolition of price controls and an increase in defense spending to 4 percent of the national budget.

In addition to a promise to denationalize industries taken over by the Socialist government after 1981, the program also called for the return to private enterprise of banks and insurance companies nationalized immediately after the war by de Gaulle. It promised to sell off the state-run electronic media, with the exception of one television and one radio channel.

Some economists have predicted that a right-wing government could have difficulty fulfilling its pledges on rapid denationalization in view of the fact that many of the companies concerned are losing large amounts of money.

The most obvious candidates for immediate denationalization, according to this analysis, are the banks and one of the three state-run television channels.

"Nobody wants to buy state-run automobile manufacturer Renault. It isn't worth anything," commented Jacques Plassard, director general of Rexeco, an independent economic research group.

While avoiding any precise commitment to bringing down unemployment in the short term, the opposition promises to lay the groundwork for renewed growth by relaxing controls. It calls for a reduction in public expenditure, the encouragement of market forces and the relaxation of exchange controls.

Other points include a promise to repeal a law on proportional representation introduced by the Socialists last year in favor of the old system of majority voting. Chirac accused Mitterrand today of manipulating the voting system to prevent a right-wing landslide.

While the opposition parties have promised to dismantle a large part of the Socialist government's heritage, there is no mention of going back on the 39-hour work week, a fifth week of paid vacation, or retirement at 60, changes generally popular among the electorate.