After studying the "dissapointingly poor" showing in last June's parliamentary election, the leadership of the Spanish Communist Party has decided to "democratize" and to bolster its Eurocommunist image for the forthcoming municipal voting.

The Communists clearly are trying to carve out new ground for themselves on a national political scene transformed by the end of four decades of dictatorial rule in Spain during which the Communist Party was outlawed and most of its leaders in exile. As they are trying to adjust to the new opennes openness in Spanish politics, the Spanish Communists obviously regard their independent, anti-MOscow stand as a way to gain public support and respectability.

The Spanish Communist do not accept thesis that the split between French Communist leader Georges Marchais and French Socialist Francois Mitterand is a blow to the development of Communist partiest independent from Moccowovnsme pendent from Moscow either in Western Europe or in the rest of the world.

Their principal concern at the moment is to "open up" the party so that there can be "greater participation by the membership." The party, a Communist spokesman said, is still organized "like an underground, with cells and rigid lines of command." He admitted that the present structure has to be scrapped because of criticism from the ranks, and predicted the election of "young Communists" to the Central Committee.

The reorganization will take place at the next party congress, which will be held early next year. The aim is to win more votes in city elections.

"That's how the people get to know us," said a Communist. "That's how the French and the Italian parties grew, by winning in the cities and running them."

All this does not mean the Spanish Communists are ignoring the differences between French Communists and Socialists. They are having a running polemic of their own with the Spanish Socialist Workers Party, Spain's second largest political force.

General Secretary Santiago Carillo, a leading force in the Eurocommunist movement, has been highly critical of the Spanish Socialists for refusing to form a coalition with Premier Adolfo Suarez and all "democratic forces" for the formulation of a common program to pull Spain out of its deepening economic and political crisis.

The position of the Spanish Communists and Socialists, however, is considerably different from that of their French counterparts since they became legal only last spring after being underground since the 1936-39 civil war.

The Socialists, led by men mostly in their 30s, have chosen to become an opposition party and are becoming increasingly aggressive in their attacks against the premier and his policies.

They won a surprising number of votes three months ago in Spain's first free legislative elections in 41 years. They believe that by taking the offensive, and shunning both the Communists and Suarez, they will do even better in the municipal races, expected early next year.

The Communists, led by Carrillo, have adopted a moderate stance on all issues.

"We won't obstruct," said a party spokesman. "We think the Socialists are mistaken, that neither they nor Suarez have the majority necessary to enact a program that will be accepted by the entire nation. Even if we formed a left coalition, we wouldn't have the votes. We are in a unique pre-democratic situation. This requires a way out involving all parties. We don't necessarily want to share power but we want to share responsibility."

Spanish Communists describe this position as purely Eurocommunist. "Our model, if it can be said that we have one" said a Communist, " is the Italian party of Enrico Berlinguer."

The Spanish Party has apparently placed all its bets on Eurocommunism and a strong show of independence from Moscow. Carrillo has gone far beyond Marchais and Berlinguer. He has attacked the Kremlin repeatedly in speeches and in his best-selling book, "Eurocommunism and the State." The Soviet Union has responded with virulent counterattacks.

Carrillo's moderation, his with and his fight with Moscow have boosted his image both here and abroad. So have invitations to go to the United States to speak at Yale University and at the Harvard-MIT Center for western European Studies. He plans to travel to New Haven and Cambridge in November.

He will be the first top Western European Communist leader to visit the United States since the 25-year-old Walter-Maccarran Act restrictions barring Communists from the United States were softened by the Carter administration.