Premier Adolfo Suarez has gone all out to win an absolute majority in Spain's parliamentary elections Thursday, but his first U.S.-style grass-roots campaign appears to be in trouble because of a combination of massive voter apathy and small bands of virulent rightist and leftist hecklers.

After meeting with rightists, who called Suarez a "traitor" to the Francisco Franco dictatorship that he once served, and leftists, who pummeled his car and told him to "get out," during a weekend tour of the poor southern Andalusia and Extremadura regions, the 45-year-old premier canceled most of his scheduled appearances last week to study future strategy. He said he was suffering from a sore throat.

Friday, under tight security, Suarez flew to Bilbao, the Basque industrial center that has been the scene of separatist guerrilla killings, for a talk with party followers. He made it a point to visit a government official who had been shot in the leg by terrorists, and avoided touring the city.

Socialist General Secretary Felipe Gonzalez, 36, who is Suarez' main rival in the first election under the two-month-old democratic constitution, has been more successful in drawing crowds. But last week in Estella, in the Basque region, Gonzalez was stoned by separatist sympathizers as he left a speaking engagement at a movie theater by a back door.

At stake in the election are 350 congressional and 208 senatorial seats. Indications are that neither centrists nor socialists will win a majority for a four-year term, and that they will probably have to work out a social and political pact to deal with Spain's economic problems and the implementation of the new constitution.

Political leaders are worried about the outbreaks of hostility toward candidates. It reminds them of the violence that effectively destroyed the Spanish Republic in the 1930s and led to the 1936-39 civil war and Franco's long and harsh reign. It also raises fears for the lives of campaigners.

Still, in the country that gave birth to the concept of macho, office seekers must show their machismo.So Suarez talked back to his tormentors, and Gonzalez defied them by calling the Basque separtist underground "fascist assassins."

The premier and his ruling Center since the week of Feb. 2. The Socialist Democratic Union party are not running on a platform. Instead they are promoting a "we deliver" image. The selling point is that they engineered the transition to democracy and, consequently, deserve a popular mandate to continue what they started.

Gonzalez's campaign pitch is moderate, too. He avoids mentioning the strong Marxist roots of the Spanish Socialist Workers Party. What he projects is a Western European social democratic image so as not to frighten the restless Spanish military establishment, which leans strongly to the right. In fact, he intends to move the party away from Marxism in its convention in May.

Center Democrats, however, hammer away at the Marxism of the Socialists in a effort to win moderates and rightists and split the Socialists into factions.

With the election less than two weeks away, Center Democrats and Socialists are running neck and neck in public opinion polls, but neither has more than 20 percent of declared voters.

A poll published yesterday by the newsweekly Cambio 16 put Gonzalez ahead of Suarez for the first time went up from 19 to 20 percent of voter preference, while the premier dropped from 27 to 19 percent.

Running far behind is the Communist Party, led by Eurocommunist Santiago Carrillo, and a new "civilized right" grouping called Democratic Coalition, headed by former interior minister Manuel Fraga and former foreign minister Jose Maria De Areilza.

The Fascist National Union Party, which upholds the ideals of the Franco dictatorship, is holding steady, and it should end up with at least one seat in parliament.

Voter surveys, however, show a disturbing constant of "undecided" voters hovering between 35 and 40 percent. The high percentage of uncommitted is a matter of concern among government officials, political leaders, and Western diplomats.

"The polls -- if they are right -- indi-cate that many people won't bother to vote," said a high Spanish official. "Apathy does not bode well for our infant democracy."

In his public appearances as he jets around Spain, Gonzalez hammers away at the issues that worry Spaniards:

Unemployment, currently at nine percent;

Inflation, at 16.5 percent;

A shortage of housing, schoolrooms and hospital facilities;

Terrorism, which claimed 79 lives in 1978 and 24 so far this year.

The premier is also the target of strong criticism by Fraga and Areilza. Their main contention is that the Suarez economic policies have caused unemployment by frightening Spanish investors and that his public order softness has encouraged terrorism.

A continuing wave of strikes for higher pay by Communist and Socialist-led unions appears to be having no impact on the Spanish voter, even though the walkouts have affected practically every industry. Some of the strikes have caused violent clashes.

Suarez and the right recently got a boost from the Roman Catholic hierarchy, which warned believers against voting for parties advocating abortion and divorce. It was the first time Spanish bishops have taken a conservative political line since Franco's death in 1975.