The Spanish Communist Party yesterday reelected Santiago Carrillo secretary general, just a day after he led a successful party move to drop the label "Leninist" from its description and move further away from the Soviet Union.

The small party's uneasy move toward a new image was clearly intended to appeal to voters in future municipal and legislative elections and modify the militant reputation it earned during the 1936-39 civil war. The Communists won only 20 of a possible 350 seats in last June's legislative elections and less than 10 percent of the vote.

At a four-day congress that ended last night - the first legal Communist Party congress since the civil war - there was bitter debate over the new image for the party sought by Carrillo, one of the most prominent advocates of a Eurocommunist "movement."

He was roundly criticized by opponents for making "name changes" when the party "must resolve fundamental problems and determine why it did not do well in the election."

The debate centered on the proposal to drop Leninism, and an issue Carrillo's supporters won Friday night with 968 out of 1,267 votes. But that dispute was but a symbol of deeper divisions.

Paradoxically, young Eurocommunists, such as Jose Maria Mohedano, said that those who wanted to get rid of Leninism were "Stalinists" imposing their views from the top. Other liberals charged that Carrillo was scuttling words while keeping tight "centralist control of the party, which is both Stalinist and Leninist."

Supporting the liberal were pro-Soviet hardliners who view Carrillo's support of Premier Adolfo Suarez and the monarchy as a betrayal of their civil war struggle and of the persecution that the party, which was legalized only last year, suffered throughout Francisco Franco's dictatorship.

A Soviet delegation - which gave Carrillo a large portrait of Lenin, whose birthday was last week - was shocked at the debate. Victor Afanasiev, editor of Pravda and member of the Soviet party's Central Committee, said it was a mistake to air internal affairs in public.

"I have never seen anything like this in any [Communist] Party congress," remarked an Eastern European journalist. "I think it's good, a good lesson for the Soviet Union."

Carrillo, who ran the convention in shirtsleeves, was quite aware that the Congress and the new policies was important not only to the future of the party but to the Eurocommunist concept he has advocated with as much passion as any other Western European Communist leader.

He has indicated, however, that the Spanish party has to make significant adjustments if it is to become a force in a democratic Spain, and that the old image and bitter memories of the civil war must be erased.

The party began to move in that direction when it dropped its demand for a Republican form of government and a republican flag and gave its support to King Juan Carlos I and the monarchy so long as it supports "democratic development."

The true test of Carrillo's latest daring move - which is likely to have repercussions throughout the Communist world - will probably be at the ballot box.