The Spanish government faced calls from across the political spectrum today for a full explanation before Congress of the confusion and contradictory reports surrounding the weekend seizure of the Central Bank in Barcelona by a gang of gunmen.

With the credibility of Spanish Premier Leopoldo Calvo-Sotelo's centrist government at its lowest level since it took office after a military coup attempt last February, Socialist and Communist parties joined forces with the conservative Democratic Coalition in parliament to demand that Calvo-Sotelo appear before legislators Tuesday. The call broke a previous tacit agreement among the country's political parties not to press the government too hard in the aftermath of the coup attempt.

Spokesmen for the opposition parties said that the formation of a more broadly based government, possibly including both Socialist and Conservatives, would be proposed during the Congress debate.

Adding to political tension, which was termed as "serious" by sources closed to the Cabinet, were reports of widespread indignation in military circles already disaffected over the alleged inability of the premier to provide firm government. Military circles were said to be angered by the government's reporting of the bank incident, which linked the seizure of more than 200 hostages for a 37-hour period to members of the security forces.

The chief government spokesman, however, said after an emergency meeting of Calvo-Sotelo and senior ministers early this morning tha it was believed the Barcelona operation had been carried out by petty criminals and anarchists masterminded and financed by ultrarightists. At the heart of the political nervousness was a growing conviction in government circles of a determined extreme right-wing effort to capitalize on the instability since February's failed putsch and to pave the way for a military takeover.

Police in Barcelona were interrogating nine alleged members of the gang that broke into the headquarters of the Central Bank Saturday and were captured by Army commandos late last night. A 10th gunman, who was described by police as having a record of sexual offenses, was killed in the rescue operation. The suspects were described at a police press conference today as being minor criminals and anarchists, aged 21 to 41, who lived in different parts of Spain.

Opposition calls for an official explanation before Congress were fueled by the confused reports that surrounded the bank raid. Contrary to previous reports of a well-armed terrorist group, armed with automatic weapons and explosives, police in Barcelona said that no explosive charges had been found in the bank and that the gang was equipped with an ancient machine pistol and obsolete, rusted handguns. In addition, official sources leaked the information during the weekend siege that members of the Civil Guard were involved and that attackers numbered between 24 and 27.

The reports, later denied, that Civil Guards who had backed the putsch were among the Barcelona gunmen provoked an angry response among the military. wThe extreme right-wing newspaper El Alcazar, which is widely distributed among military officers, termed "intolerable" the attitude of the civilian defense minister, Alberto Oliart, who had strongly hinted at the weekend that the paramilitary guardsmen were involved in the bank raid.

Sources close to the military said some officers believed that the Barcelona incident was an attempt to frame the armed sevices and provoke public hostility toward them. Military restiveness has been compounded by growing criticism of the government's handling of law and order since the coup attempt. Over those months, there have been sustained terrorist attacks by extreme left-wingers aimed principally at military figures and policemen.

Government sources reported genuine official concern over the alleged ultrarightist financing of the Barcelona gunmen. It was believed that several meetings had been held in the town of Perpignan, just across the border with France, between the gunmen and their backers. The attackers, who proclaimed themselves loyal to the leaders of the failed putsch and chose to strike just three months afte rebel guardsmen had taken Congress hostage, seemed primed to gain maximum publicity and achieve optimum destabilization, these sources said.

The normally progovernment Diario 16 newspaper in Madrid said in an editorial today that should there be confirmation of extreme rightist manipulation, Spain was set on a "Turkish" course in which the armed forces would be called upon to settle the instability.