Three years after its legalization in Holy Week 1977, the Spanish Communist Party stands at a crossroads.

The party has achieved tolerance, respectability and a degree of acceptance among Spaniards that are a far cry from the repression and witch hunts under the late Francisco Franco. Yet, while part of the new Spanish system of representative government, the Communists nevertheless wield little or no effective power.

Their satisfaction at being able to enjoy the fruits of legality is tempered by frustration at the lack of electoral success. The Communists have failed to capitalize on their record of having been in the forefront of the opposition to the Franco regime,, and their moderate Eurocommunist policies have little impact on a young electorate that is essentially reformist and progressive.

For all the Spanish Communist Party's Eurocommunist protestations and all the periodic rows between the party's secretary general, Santiago Carrillo, and Moscow -- the latest caused by his condemnation of the Soviet Union's invation of Afghanistan -- and for all the talk of moderation, democratic socialism and national reconciliation, the party's image remains rooted in a past that is rattling with Stalinist skeletons.

On the third anniversary of becoming an officially recognized political party, the Spanish Communist Party appears to be suffering a quantitative and qualitative drop in its membership in what seems like firm evidence of disenchantment with the party's leadership and strategy.

According to the magazine La Calle, which is sympathetic to the party, membership was 201,757 in 1977 and fell to 171,332 a year later. The magazine estimated that by last October a further 30,000 card-carrying members had either left or failed to renew their affiliation, leaving the total membership at about 140,000.

A spokesman for the Communist Party admitted that the figures were realistic, but said the party had only 15,000 members when it was legalized, and this had been followed by a massive increase in membership. The spokesman said that membership figures had been "inflated," but now the "half-committed" members had quit, leaving a more disciplined and coherent party.

More indicative of a possible crisis than the total number of members is the defection of key party supporters. One is Madrid lawyer Jose Maria Mohedano, who joined the party as a student leader in the mid-1960s and recently announced that he was leaving it. His chief complaint is with the party's leaders, and the absence of political debate.

"My move out of the party is not an isolated incident," he said in an interview. "Many people who were active politically in the '60s and '70s are quitting. In the last three years membership is down 30 percent."

Mohedano achieved a certain recognition as a defense lawyer in cases against leftists in Franco's political courts. Recently he took part in a suit against a fascist group convicted of attacking a Communist legal advice center and killing five persons.

Mohedano is critical of the party's aged leadership. Alone among Spain's political parties, the Communists retain at the top people such as party president Delores Ibarruri, the legendary "Pasionaria," and Carrillo, who were household names during the Spanish civil war. Of the 35-member executive committee, 22 are more than 50 years old and 17 are more than 60. Mohedano says this leadership is "the same one that built an ideology and an organization on the Stalinist model."

"There have not been any internal strategy debates within the party," said Mohedano, who accused its leaders of failing to adapt to the open politics that accompany the "democratic road to socialism," or "Eurocommunism," which the executive committee officially espouses.

The lack of political debate, and particularly the failure of Eurocommunism to strike electoral roots, has alienated young intellectual and white-collar supporters, as evidenced by open references within the party to a "crisis of college graduates and members of liberal professions among the Communists' supporters.

The decision to legalize the Communist Party was perhaps the most controversial one that Premier Adolfo Suarez made along the rock road that led to the restoration of political liberties in Spain.

Hoping the Communists could just tiptoe into the political scene, he announced the decision on the quietest day of the Spanish political calender -- Holy Saturday -- which in 1977 was April 9. Holy Saturday traditionally is a day when all of Spail takes a holiday in preparation for Easter Sunday. But for all the timing, or else because of it, the storm broke over the premier's head.

Suarez had been forced into legalizing the Communists by the threat of an opposition boycott in the general elections -- Spain's first free vote in 40 years -- that were to take place in June 1977. In a series of secret meetings with Carrillo he extracted from the Communist leader a pledge of allegiance to the crown.

Carrillo proved a model of moderation and patriotism. He told his supporters the issue was not republic versus monarchy, but democracy against dictatorship. He insisted that the national flag be present at meetings and abandoned the republican banner.

He refused to use the clenched-fist salute, dropped inflammatory rhetoric from his speeches and spoke about national reconciliation. But the election results were a shock to the Communist strategists.

As the strongest, best organized clandestine force during Franco's rule, and the spearhead of opposition to the regime, the Communists expected to emerge as Spain's major leftist party. Instead, they picked up only 9.2 percent of the vote and 20 seats in the 350-member Congress, compared with 29 percent of the vote and 118 seats won by the Socialist Party.

In last year's general elections the Communists inched forward to 23 seats; the Socialists won 121. It appears evident that for the foreseeable future the Communist Party is unlikely to get more than 10 to 11 percent of the popular vote.

The Communists could take some comfort from the fact that after the 1977 election they were actively consulted by the government as Suarez strove to consolidate democracy and avoid partisann political confrontation. But the past year has seen the Communist Party's growing isolation.

The Socialist's who style themselves as the alternative government to Suarez's ruling Union of the Democratic Center, have kept their distance from the Communists and rejected Carrillo's urging to join with the centrists in a coalition Cabinet of national unity to solve the worsening economic situation.

A Socialist Party congress last year also ruled out any possibility of future pacts with the Communists and reinforced the positions of the Social Democrats at the expense of more radical members who favored unity among Spain's leftists.

The Communist Party's aspirations have been checked by the emergence of a strong, organized Socialist Party with younger leaders and clear ideas about resisting Communist pressure. Calls for unity and for coalition governments are viewed by the Socialists as traps aimed at either blurring the differences between the two parties or leaving the field clear for the Communists.

Despite the century-old socialist tradition in Spain the Socialists Party is a young party, led by the post-civil war generation that cut its political teeth in the twilight of Franco's government. Accordingly, one of the main problems the Communists face could be -- as the dissidents suggest -- the nature of the Communist Party's leadership.

The irony of all this is that it was the skill of the 65-year-old Carrillo that kept the party together during the dark years under Franco, yet it seems unable to produce results in this period of legality.

But Carrillo's grip over the party is so strong that any change seems unlikely and there is no obvious heir among the half-dozen younger members of the party's executive committee.

There was little for the Spanish Communist to celebrate on this anniversary beyond congratulating themselves on the fact that they are no longer persecuted. Having come in from the cold three years ago, Carrillo and his followers find themselves still on the outside looking in.