There was a heady moment at the recent Spainish Communist Party Congress. Party leaders permitted their opposition to speak for 35 minutes on a major issue, even though party rules would have allowed them to squesch, this maysayers. This relaxation of the rules set off feverish chapping and cheering by both delegates and leaders in an orgy of self-congratulation, as if everyone were saying to each other: democracy at last.

But such sentiments were premature. The party congress, the first on Spanish soil since 1932, may have been more free and open than any other Communist meeting in history. But there still is serious question whether Spanish Communists understand and practice democracy.

Actually, Secretary-General Santiago Carrillo and his lieutenants controlled the congress at all important stages. Minority views were rarely heard at open sessions. A new central committee was elected without announcing any candidate's total votes. Some of those who opposed Carrillo at the beginning of the convention were punished at its end.

It is probably unfair to assess the Spanish Communists' democratic attitudes by their four-day April congress. The conventions of any political party - or of any large association - are rarely sterling examples of democracy. The 1964 Democratic National Convention under Lyndon Johnson and the 1972 Republican National Convention under Richard Nixon would probably have failed a strict test of democracy. So, too, might the conventions of most American labor unions. It is easy for leaders to manipulate a large organization and too hard for individual members to band together to dislodge the entrenched few at the top.

Moreover, the Communists probably are no less democratic than any other Spanish political party, all of which are either newly formed or operating legally for the first time since the dictatorship of the late Francisco Franco.

The parties simply have not had time to develop democratic procedures. In fact, it is doubtful that the upcoming congress of the Union of the Democratic Center - Spain's largest party - will be as free and open under the leadership of Prime Minister Adolfo Suarez as the Communist congress was under Carrillo.

Yet this "unfair" test has to be applied to the Spanish Communist now, for there is no other way of measuring their democratic attitudes, and gauging those sentiments is too vital to leave aside.

Carrille is the foremost exponent of Durocommunism. He insists that he and his party believe in European-style parliamentary democracy and will seek power only through the ballot box. Once in power, according to Carrillo, the Communists would maintain the democratic parliamentary system. If voted out in a subsequent election, he claims, they would leave office peacefully.

Since there exists no state that is both Communist and democratic, Carrillo's position has provoked a good deal of skepticism. Analysts scoff at the idea that Eurocommunism is anything more than a tactical subterfuge, a way of achieving power in a democracy before destroying it. To counter this, the Eurocommunists can only show, through the way they organize and run their own parties, that they do understand democracy and practice it.

It is Carrillo's view that the Spanish Communists have passed the test. At the end of his party's congress, Carrillo told the delegates that their conference had been "a historic congress, because it is the first congress in legality and because it had been a profoundly democratic congress, as never before in our history."

Certainly, any assessment of democracy within the Spanish Communist Party must take into account the 63-year-old Carrillo's personality. Despite his avuncular manner, he is a tough, authoritarian man with a history of firm leadership and shrewd organization.

In the days of the Spanish Republic, he organized the Socialist and Communist youth into the one group under his leadership. During the Civil War, while still a young man, he was appointed a member of the Committee of Defense that steeled Madrid to resist Franco's advancing armies. While leading the clandestine Spanish Communist Party from exile in Paris, he ruled with an iron hand and expelled dissenters.

These old habits halped Carrillo during the months before the congress, when he travelled throughout Spain to attend the preliminary regional conferences where the selection of delegates to the congress was taking place.

The issue that served as a touchstone was Carrillo's insistence that the party drop its Leninist label. Otherwise, in Carrillo's view, few voters would ever accept the party's contention that it was democratic. But Carrillo's heavy-handed lobbying for this change irked some dissidents.

"They are using Stallnist methods to democratize the party," said one angry Communist in Barcelona.

Since the regional conference did not use proportional representation in electing delegates to the congress, the anti-Carrillo minorities were probably underrepresented on most delegations. Thus, at the end of his weeks of travelling and lobbying, Carrillo was assured of a congress that, at least on the major issues, would cause him no trouble.

Indeed, the most significant debate during the congress occurred behind closed doors. After listening to Carrillo's opening report on the party's progress, the delegates discussed it in regional and provincial caucuses. There may have been heated argument in these caueuses, but an outsider could find no sign of it later.

There was a chance for more debate in the procedure used to adopt the party's new statutes and "theses." The theses are offical statements of ideology and policy - a kind of party platform - and the most controversial, Thesis 15, was to abandon the Leninist label in favor of a new description of the party as Marxist, democratic and revolutionary.

Under party rules, the committee spokesmen presented the theses and statutes as approved by a committee and offered arguments in their favor. The minority view was then presented only if it had managed to win more than a third of the votes in committee. But one exception was made.

In the case of Thesis 15, the minority fell short of a third. Nevertheless, because of the importance of the issue, party leaders agreed to let the minority present its argument. This was the decision that set off so much self-congratulatory applause and cheering.

The election of a new central committee was left largely in the hands of a nominating committee. The delegations, depending on their size, assigned either one or two representatives to the nominating group. But Carrillo, through his influence on most delegations, controlled the nominating committee.

Along with removing its Leninist label at the congress, the party also threw out the old Leninist rule that its affairs would be run by "democratic centralism," the old Communist idea that the leaders have the right to make important decisions in the name of party militants. Instead, according to the new statutes, the party is to be run by "democratic rules."

The Communists obviously have liberalized party procedures and have made democracy their professed goal. But a good deal of authoritarianism and a democratic centralism remain. The Communists still have a way to go before they can quiet the skeptics and scoffers.