The Spanish government is coming under heavy fire at home for advancing the date of Spain's official entry into NATO.
Early Sunday morning Spain ended more than a century of international isolation and a tradition of neutrality that kept the country out of two world wars in this century.
In a surprise move, announced only hours before, Spain officially became the 16th nation to belong to the North Atlantic Treaty Organization (NATO) when the Spanish embassy charge d'affaires, Alonso Alvarez de Toledo, delivered the Spanish government's confirmation letter to United States Under-Secretary of State, Walter J. Stoessel Jr. at the State Department in Washington.
Spain's early entry caught most political observers by surprise as the event was expected to coincide with the official ceremony in Brussels at NATO headquarters on June 5, when the Spanish flag will be raised in the presence of Spanish defense and foreign affairs ministers and representatives of other NATO members.
Criticism of the event was almost immediate. The opposition Socialist Workers' Party termed the move ''an historical mistake that we will have to pay.'' Only two days earlier, the socialists had presented, and lost, a parliamentary motion to delay NATO entrance until the issue of Gibraltar's sovereignty was negotiated with Britain.
Fernando Moran, the foreign affairs spokesman for the socialist party, said he thought official entrance had been speeded up to avoid further public discussion of NATO membership before the Gibraltar negotiations.
The Falklands war has stirred up public opinion for Spanish sovereignty of the Rock. ''The government wants to avoid all debate on the issue,'' Mr. Moran insisted, ''and Sunday's surprise entry avoids further insistence on another petition for parliamentary debate to delay alliance membership.''
NATO membership has been one of the major pillars of Prime Minister Leopoldo Calvo Sotelo's foreign policy. This policy constantly faces opposition, however. There is reticence even within the ranks of the ruling party itself, the Union of Democratic Center (UCD). The political council of UCD is to meet June 5 and 6, the date of the Spanish NATO entrance ceremony, and there has been some speculation that Mr. Calvo Sotelo wished to avoid internal, party bickering over delaying alliance membership.
Former Premier Adolfo Suarez had taken a deliberately wishy-washy stance on NATO, and his supporters have not been enthusiastic over entering the Western alliance.
The Suarez faction of UCD has been gaining in popularity after regional Andalusian election results that were disastrous for the government and gave an absolute majority to the socialists and a mere third place--with only 13 percent of the vote--to UCD.
Spain's long tradition of neutrality in international conflicts explains some of the shyness in joining NATO, as well as open hostility to a Western military alliance in which, paradoxically, the extreme right and left coincide.
Many Spanish politicians feel NATO membership will mean unequivocal support of other NATO members engaged in other conflicts such as the present Falklands crisis, in which Spain has generally supported Argentina. Foreign Affairs Minister Jose Pedro Perez Llorca said, however, that as a member of NATO ''Spain will exercise its right to veto to defend Spanish interests,'' a direct reference to third-country conflicts in which NATO and Spanish interests may not coincide.
The first test of Spanish independence may come at the NATO Summit meeting June 8 and 9. It is not inconceivable that NATO may push a resolution against Argentina or in support of member country Britain if the Falklands crisis continues. Spain will find it difficult to support any pro-Britain stance as the present Spanish position is leaning heavily toward Argentina.