Spain's ruling party hangs on by a thread

With only months to go before probable national elections in the fall, Spain's ruling center party has barely survived disintegrating into three or more different parties.

The latest round of internal turmoil increases the probability of a Socialist electoral victory. But it also signals that Spanish democracy may be drifting toward an eventual two-party system of conservative coalitions versus social democratic coalitions, with a greatly reduced hinge party at the center.

Both the Spanish left and right have been making efforts at moderation and have moved toward the center, picking up sympathizers at both ends of the hodgepodge government center party, the Union of the Democratic Center (UCD). The mainstream left is no longer Marxist and the mainstream right is no longer fascist.

In the present crisis, two conservative factions of the UCD threatened massive desertions to form coalitions or alliances with the conservative party, Popular Alliance, led by Manuel Fraga. Likewise, the Suarist centrist faction threatened to walk out and form a post-electoral alliance with the Socialist Party if UCD turned too far to the right in an attempt to keep conservatives within the fold.

Party unity was maintained, but three new political parties, representing the warring factions, were founded anyway. This indicates that coalitions to the right and left of the government party have the possibility of forming in time for the coming elections.

The new parties were founded during the five-day crisis to attract expected deserters of the UCD or sympathizers from other parties. The Popular Democratic Party, representing Christian Democratic tendencies, and the Liberal Democratic Party, representing traditional free-market Liberal policies, were formed on the right. On July 13 the Suarists created a new party, Social Democratic Center. Adolfo Suarez Gozalez didn't even bother to attend the UCD political council meeting, although some of his followers called for his return.

Although UCD leaders claimed there was still room for a center political party, no one seemed very convinced or even optimistic. Most of the Spanish press has warned the squabbling party against creating the impression of another ''power vacuum'' that could be used as an excuse by the military for another coup attempt. The last coup, in February 1981, failed.

Warding off the specter of another coup, former Deputy Premier Fernando Abril and Suarez supporter, stated that he was ''fed up with coup risks,'' answering criticism of the ''destabilizing effect'' of the UCD crisis. ''Its about time to tell the military and bankers to mind their own problems more and to mind less the problems of others.''

Meanwhile, the gradual suicide of UCD may, in the end, clarify the Spanish political system if two moderate alternatives eventually emerge.

Mr. Fraga, for example, harbors big hopes of forming a winning electoral coalition with deserting or sympathetic UCD conservatives.