The French government majority was reelected yesterday with a broad margin of 288 National Assembly seats against 199 for a Socialist-Communist opposition that was considered a certain winner less than 10 days ago.

The results make rule in France by the same Western-oriented forces that have ruled the country for decades seem certain and make it unlikely that France will take the radical turn to the left that was worrying the major members of the Atlantic Alliance.

The tide against the leftist opposition began to build a week ago, when government forces almost matched the vote of the left in first-round elections. At that point, a victory for the backers of President Valery Giscard d'Estaing in yesterday's vote was generally assumed.

Even so, the showing by Giscard's backers yesterday was far larger than predicted. Where there were fears of sharp erosion in the government position prior to the first round of voting, the government will end up with almost as many deputies in the new assembly as it had in the outgoing one.

A large number of Socialist voters did not follow their party's recommendations to transfer their votes in the runoffs to Communist candidates who outpolled Socialist ones in the first round election.

Leftist unity started falling apart almost immediately, starting with the statement by Robert Fabre, leader of the Radicals of the Left, the Smallest and most moderate of the three leftist partners, that he no longer feels bound by the joint program signed in 1972.

Fabre also hinted that he would be open to offers from Giscard.

The majority's 288 seats were divided into 145 for the Gaullist party, 137 for the new centrist-Giscardist party, the Union for French Democracy, and four other progovernment deputies.

The left's 199 seats were divided into 102 for the Socialists, 10 for the Radicals of the Left and 86 for the Communists. There are still four seats to be filled from French islands in the Western Hemisphere.

Except for the Gaullists, all four major groups gained some seats. In the outgoing assembly, the majority had 292-173 for the Gaullists and 119 for the centrists and Giscardists. The left had 182-92 Socialists, 13 Radicals of the Left, 74 Communists and three other deputies.

For the first time, Giscard will have a force of his own in the assembly roughly equal to the Gaullists. Also, for the first time in the Fifth Republic founded by Gen. Charles de Gaulle in 1958, the Gaullists will not be the dominant party in the governmental majority.

The nearly equal division of the country between left and right was a recurring theme in the commentaries last night of political leaders and analysts.

Giscardists spoke of the need for social reforms and the need to extend an open hand to those who voted for the left. Giscard himself is expected to elaborate on that theme when he addresses the country Wednesday. He may also give some indications of what kind of a cabinet he will be name and its program.

Giscardist spokemen, starting with Prime Minister Raymond Barre, called the government's victory a justification of Giscard's political strategy of letting the assembly finish its five-year term without dissloving it beforehand for early elections.Those comments were aimed at Gaullist leader Jacques Chirac who had called on the president to dramatize things by calling early elections.

Socialist leader Francois Mitterrand led a chorus of Socialist leaders in blaming the left's defeat on the Communists tactic of attacking the Socialists over the past six months.

"History will judged as it should those who are responsible," said Mitterrand. He recalled that the left won the first round of voting last Sunday even though the government will have a majority of assembly seats.

Last week, the final returns showed that 82.8 of the eligible voters had gone to the polls - a record for a legislative election under the Fifth Republic. This week, the final returns are expected to show a turnout of about 85 per cent - and all-time record for any election under any French republic. Most of the new voters yesterday apparently voted for the government candidates.

The first major concern of any new Cabinet is bound to be how to deal with the demands of the labor unions.

Gearges Seguy, the Communist leader of the 2-million strong General Labor Confederation, the largest French union, called on the government last night to honor its electroral promises to the workers. He asked for immediate national negotiations to raise the minimum wage, give employees a fifth week of paid vacations, the creation of new jobs and the institution of the five-day, 40-hour week.

All those were points in the left's joint program that at least some government leaders said they were willing to consider. Socialist leaders Mitterrand and Pierre Mauroy, and the popular Michel Rocard won easy reelection, as did Communist leader Georges Marchais and Left Radical leader Fabre.

Most of the top government leaders were elected last week among the 68 deputies who got more than half the vote on the first round.

Former interior minister Michel Poniatowski, a close Giscard associate, was defeated. Alexandre Sanguinetti, a prominent Gaullist, also lost his seat.

Jean-Jacques Servan-Schreiber leader of the progovernment faction of the Radical Party, won his race in Nancy by only 22 votes and his Socialist opponent demanded a recount. In Reims, Jean-Louis Schneiter, the centrist candidate, defeated the Communist mayor, Claude Lamblin.

Jacques Soustelle, prominent Gaullist who became an ardent opponent of Gen. de Gaulle's abandonment of French Algeria and who had reentered parliament as a centrist after returning from exile, was defeated in Lyons.