Conservatives Aim for Comeback. But veteran leader may find ties to former dictatorship too great a political liability. SHAKING UP SPANISH POLITICS

ONLY two years after he bade a tearful farewell to politics, former opposition leader Manuel Fraga has again been acclaimed by Spanish conservatives as the president of the party he founded. Mr. Fraga's comeback included promises to revamp the 11-year-old Popular Alliance, renamed the Popular Party at a special two-day party congress in Madrid last weekend.

The party retains its respect for the Roman Catholic Church, reflected in conservative stances on social issues such as abortion and support for parochial schools. But there were indications at the conference of a move away from big business in favor of populist critiques of the government's free-market economic policies.

The veteran conservative leader's goal is to construct a broad center-right grouping capable of unseating the Socialist Workers' Party of Prime Minister Felipe Gonz'alez M'arquez in general elections to be held by June 1990.

He hopes to take advantage of deepening conflicts between the Socialist Party and its affiliated trade union, reflected in a successful one-day general strike last month called to protest alleged pro-business policies and Spain's 19 percent annual unemployment rate. The union, believed to control about 1.5 million of the 8 million votes the Socialists won in 1986, has threatened to withhold its backing in the next elections.

One major obstacle to Fraga's plans to displace the Socialists may be centrist former Prime Minister Adolfo Su'arez, credited with steering Spain back to democracy after 36 years of right-wing dictatorship.

The Social and Democratic Center Party that Mr. Su'arez heads was moved up in a recent opinion poll with about 13.7 percent support, while the Popular Party slipped slightly to 20.8 percent support, compared with 37.5 percent for the Socialists.

Su'arez has repeatedly rejected any deal with Fraga on the national level. Without his support, there is little chance for Fraga to oust the Socialists in the next general elections.

A tourism and information minister under the late Gen. Francisco Franco, Fraga has led a political career that has sparked controversy.

Fraga is said by political commentators to have a vote ``ceiling,'' meaning that many Spaniards would not vote for him under any circumstances. But he is also credited with a pull that guarantees a significant voting bloc. Spanish conservatives are betting their future on this.