Spain's Socialist Prime Minister Felipe Gonzalez pledged today that his government would not stage a referendum on continued membership in NATO this year because he does not want to weaken the alliance at a time of tension between the West and the Soviet Bloc.

Speaking at a press conference at his official Moncloa Palace residence to mark his first 100 days in office, the 41-year-old leader made his most forceful statement to date on Spain's commitments to western defense.

As opposition leader, Gonzalez criticized the previous government's decision to enter NATO last summer, and a Socialist promise during last October's election campaign was to hold a popular vote on withdrawal from the alliance.

Referring directly to the Strategic Arms Reduction Talks in Geneva, Gonzalez said: "I do not want it ever to be said of this government that it made the western position more fragile while East-West negotiations are taking place at this moment, negotiations which will become more tense in the coming months."

On the subject of a recent poll published here indicating that 61 percent of Spaniards wanted to withdraw from NATO and that only 8 percent wanted to remain in the alliance, Gonzalez said the findings of the survey had not suprised the government, adding that they reflected Spain's longstanding political and military isolation.

Despite the poll's results, Gonzalez said, "We are not going to provoke any alteration in NATO's political framework while the period of extreme East-West tension continues to exist in 1983 and possibly during part of 1984." He reiterated a Spanish position, adopted by the previous government, against the deployment of nuclear missiles in Spain, but he added that his government would not "take sides over the deployment of missiles in any other NATO country."

The small Spanish Communist Party and extreme leftists within the Socialist Party itself have recently stepped up their calls for the government to live up to its electoral promise on a NATO referendum. Gonzalez refused at the press conference to be drawn into a specific timetable on such a poll.

One of the first acts of the new Gonzalez government in December was to freeze negotiations on Spain's role in the alliance's integrated military command structure. Gonzalez said that following that initial move his government was prepared to take its time on the wider issue of complete withdrawal. He said that in carrying out such a reappraisal "we will certainly not prejudice the interests of the western world that we form part of."

Answering questions on Central America, Gonzalez said Spain was prepared to offer its good offices as a potential mediator should it be asked to do so by "friendly and sister nations" in the area. He stressed, however, that "up to the present moment and speaking officially Spain has neither offered itself as a mediator nor has received any proposal that it should do so."

Gonzalez is considered an expert on Central American and Latin American affairs and has visited Andean and Caribbean nations in past years in his capacity as vice president of the Socialist International with special responsibility for those regions.

Fuelling speculation that Spain might assume some form of mediating role, Gonzalez disclosed at the press conference that he intended to visit Colombia and Venezuela in May.

The Spanish prime minister is also due to hold talks here with Cuban Foreign Minister Isidojo Malmierca later this week and will meet tonight with Mexican Foreign Minister Bernardo Sepulveda.