Loud talk of splitting Swiss government coalition faded when it came time to vote

The atmosphere was unusually tense for peaceful Switzerland as Social Democrats poured into the high-ceilinged Congress Hall in the country's quietly dignified capital of Bern at the weekend.

They came from all corners of the republic to decide on Switzerland's biggest potential political crisis in a quarter-century: whether to break with the ''magic formula'' that is largely responsible for their country's extraordinary degree of economic and political stability.

The formula ensures that all four major parties are represented on the governing seven-man Federal Council and that divergent linguistic, political, and religious groups have a say in decisionmaking.

The crisis was precipitated last December when Parliament rejected Lilian Uchtenhagen, a highly qualified economist and parliamentarian, as the Social Democrats' official candidate for the council. She would have been the first woman to sit on the council. Many women were outraged at the vote.

But Social Democrats had been unhappy with the ''magic formula'' for years. More and more they came to feel they were getting a bad deal on social security, the environment, nuclear power, and women's issues.

Some were determined to teach the conservative parties a lesson and go into opposition. A speech by Mrs. Uchten-hagen called for unity. Nevertheless, when the Social Democrats met Saturday, they opted for caution: Delegates voted 779 to 511 to remain in the coalition.

Despite the vote to remain in the Federal Council, party president Helmut Hubacher warned: ''Things will never be the same again.'' He promised a harder line on the issues. But to keep many activist members in the party, he will need to keep his promise.