Chancellor Helmut Schmidt and his left-center coalition government won a clear victory in West Germany's parliamentary election today, gaining an increased majority over combined conservative opposition forces led by Franz Josef Strauss.

The increase was due largely to a stunning performance by the coalition's junior Free Democratic Party, however, rather than by gains for Schmidt's own Social Democrats.

According to a near-final tally, the government increased it's tight, 10-seat majority by 35 seats in the 497-seat lower house of parliament.

government leaders saw the results as an endorsement of the coalition's foreign policy of detente and its success in curbing inflation. "I am very satisfied and the coalition can also be satisifed," Schmidt told reporters at party headquarters. "I'm quite sure our neighbors in the north, south, west and east are very pleased with the results. Germany remains predictable, and that's the important thing."

Schmidt, 61, who has led West Germany for six years, is widely credited with increasing Bonn's clout in the political and economic councils of Europe as no other postwar chancellor. Urbane and outspoken, Schmidt represents a more assertive and self-confident West Germany. But he is considerably more popular at home than his left-of-center party.

At the same time, the bullish, provocative Strauss, a controversial figure on the West German political scene for more than 20 years, apparently scared off votes from his conservative coalition.

Faced with a choice between "stopping socialism" and "stopping Strauss" -- as the campaign slogans said -- a number of voters seemingly opted for the middle alternative of the Free Democrats, led by Foreign Minister Hans-Dietrich Genscher.

Opposition leaders were consoled by the fact that they retained the largest single voting bloc in parliament.

Under sunny skies and cool autumn weather, 88.6 percent of West Germany's 42.8 million voters went out to mark their ballots, not for Schmidt or Strauss directly, but for their parties. Half of the parliament is elected directly, and half is chosen by statewide party lists.

The Social Democrats won 42.9 percent of the vote, up three-tenths of a percentage point from four years ago, and Genscher's party won 10.6 percent, up 2.7 percentage points from 1976, its strongest showing since 1961. The Christian Democrat-Christian Social Union opposition received 44.5 percent, down 4.1 percentage points. The new environmental party, the Greens, scored 1.5 percent, far below the 5 percent minimum necessary for representation in parliament. Other smaller groups got the remaining .5 percent.

Strauss campaigned agressively on the slogan, "Peace and Freedom." He criticized the Schmidt administration for accelerating the national debt, cast doubt on the fiscal soundness of the state after 11 years of Social Democratic rule, attacked the government's approach to terrorism in the aftermath of last week's bombing at the Munich Oktoberfest and characterized the government's policy of detente with the Eastern Bloc as bringing West Germany under Soviet influence.

Ultimately, however, Strauss and the opposition coalition could not get away from the issue of Stauss' own personality, which has long aroused deeply antagonistic feeling outside the state of Bavaria, where he is state premier.

Part of this anti-Stauss reaction was simply a clash between north and south Germany. Strauss' exuberant manner is typical of southern Germany, but contrasts sharply with the more serious mood of the north.

Most of the reaction, however, had to do with Strauss himself. His basic stand as a fiscal conservative and law-and-order man, which seemed to grow exaggerated by the force of his own oratory and volatile personality, making him appear to some as dangerously dictatorial. He is believed to have frightened off particularly a number of women and young voters.

Schmidt and the Social Democrats played on these fears, portraying Strauss as a demagogue who would be prone to lose control as chancellor and could seriously challenge Bonn's fine web of international relations, especially those with its communist neighbors.

Strauss frequently countered during the campaign by describing the public relations-minded Schmidt as a better "showman" and himself as the better "politician."

Today's defeat is expected to remove Strauss once and for all as a national contender for the chancellor's post, although the 65-year-old political professional -- who like Schmidt has held the jobs of defense and finance minister -- has had a way of staging comebacks.

As unchallenged head of the Christian Social Union in Bavaria, Strauss at least has a sure political base to return to. "I've not just got a political life behind me," he told reporters, "I've got one in front of me. I am and will remain Bavarian [state premier]."

For the vastly larger and more moderate Christian Democratic Union, however, which operates in the rest of West Germany, a heated leadeship struggle is now expected.

The contest will pit Helmut Kohl, the bespectacled 50-year-old current party chairman generally regarded as a skilled organization man but a colorless personality, against a crew of young, ambitious state governors.

As for the new government, Schmidt has made clear that he is not planning any major Cabinet reshuffle. Moreover, the Free Democrats, who already had the key ministries of foreign affairs, economics, interior and agriculture, said tonight that they would not seek additional posts. The administration's post-election program will not be settled until November.

Despite West Germany's position as the economic powerhouse of Europe and Bonn's growing leadership role in world affairs, Schmidt is likely to have less maneuvering room in the near future.

On the domestic front, his chief task will be drafting as 1981 budget under very strained conditions. The financial demands on Bonn have been over-loaded with extra calls for aid to Turkey, Poland the Third World.

Additionally, Bonn has agreed to take on a greater share of the European Community's budget to offset London's smaller share, and it has increased defense spending to meet its pledge to NATO.

At the same time, higher oil prices and rising unemployment have limited the financial resources available.

Hampered by a weakened home economy resulting from high domestic interest rates and recession-damanged world markets, Bonn is being forced to squeeze its purse strings -- although West Germany continues to enjoy a positive economic rate of more than 2 percent, an employment rate under 4 percent and an inflation rate under 6 percent.

In foreign policy, too, Schmidt can expect to run up against unusually frustrating constraints. The continued Soviet occupation of Afghanistan and uncertainty over how events in Poland will unfold have put a damper on Bonn's relations with the communist states of Eastern Europe. The Iraqi-Iranian war and the sputtering of the Egyptian-Israeli talks on Palestinian autonomy have complicated Bonn's developing involvement in the Middle East.