Heavily armed gunmen sized about 250 hostages in a major bank in Barcelona today and demanded the release of four officers arrested three months ago in an attempted military overthrow of the Spanish government.

About 1,000 police and antiterrorist forces surrounded the Central Bank in the center of Barcelona, Spain's second-largest city.

Nine hostages were freed last night, including two who were taken away in an ambulance. That brought the number of released hostages to about 70.

Gunmen earlier had released a bank employee wounded during the takeover and about 20 other hostages suffering from shock. Witnesses estimated that about 40 additional hostages were released about two hours later, including one evacuated by ambulance, in exchange for food parcels from the Red Cross.

The gunmen -- numbering about 20 and described by police as rightwing extremists -- threatened to begin shooting hostages Sunday if the four officers were not freed and a plane provided to fly the gunmen and officers to Argentina.

Lawyers for the officers said their clients were not associated with the bank seizure and did not want to flee the country. Argentina refused to accept the gunmen or officers. It was not known whether this information had been given to the gunmen.

Released hostages told reporters that as many as half the 20 to 25 gunmen appeared to be members of the paramilitary Civil Guard. Hundreds of guardsmen participated in the attempted coup in February.

Barcelona Police Chief Enrique Mosquera talked by telephone with the gunmen, and one government official said a hostage bank cashier was being used as a go-between in indirect negotiations, but that no substantial progress had been made.

Premier Leopoldo Calvo-Sotelo, whose government has been buffeted by terrorism and coup scares during the past three months, held emergency consultations with senior ministers.

Afterward, the Interior Ministry issued a statement saying the government would be "absolutely firm in the face of this criminal act"

[In Washington, the State Department condemned the takeover as an "act of terrorism," The Associated Press reported. State Department spokesman David Nall also said no Americans were believed to be among the hostages.]

The seizure of the bank dramatically underlined the continuing instability in Spain, which Spanish commentators say is discrediting Calvo-Sotelo's government and keeping the main participants in the attempted coup in the limelight.

About 200 Civil Guard troopers followed Lt. Col. Antonio Tejero Molina, the leader of the attempted takeover, into the parliament building last February. All have been released -- government officials said the guardsmen had been duped by their commanders -- and the Civil Guard denied any of its men were involved in the bank takeover. However, Barcelona's military governor, Maj. Gen. Luis Saez, said he had received reports military men may be involved.

The defense attorneys for the accused officers, meanwhile, speculated that the gunmen could be provocateurs trying to turn public opinion against the officers arrested following the coup attempt.

They said the officers condemned the bank seizure as "absurd and delirious." Lawyers said Tejero, told them he had no desire to flee "under any circumstances."

Tejero has achieved folk-legend proportions since the February coup attempt. For the rightist extremists, he is the chief exponent of the traditional "sacred duty" of the military officer here "to save Spain." For moderates, Tejero represents the continued threat of a coup.

Earlier this month, a series of leftist terrorist attacks in Madrid and Barcelona aimed at military officers and Civil Guardsmen severely tested the centrist government formed by Calvo-Sotelo after the coup attempt. The military pressured the Cabinet to curtail civil liberties, introduce censorship and outlaw radical parties in the Basque country that are allegedly linked to gunmen of Basque guerrilla groups.

News services added the following from Barcelona:

The takeover began about 10 minutes after the bank opened at 9 a.m. Men armed with submachine guns, high-powered rifles and explosives entered the bank, donned masks and began rounding up employees and customers. Released hostages said the gunmen identified themselves by numbers instead of names and fired warning shots.

Bank employee Ricardo Martinez Calafell, 32, who was wounded in the leg during the takeover and released, told reporters the gunmen had placed explosives in several parts of the building, threatening to set them off if police tried to storm the bank.

One government official said food and cigarettes had been taken in for the hostages as well as a television set and a transistor radio requestd by the gunmen.

Police said all lights were on in the bank during the night, and that the hostages had been herded in front of the doors, apparently to discourage attempts to storm the building.

Notes left in various places for Barcelona newspapers said if the gunmen's demands were not met, they would kill 10 hostages immediately and one hostage every hour after that.

One bank employe released by the gunmen, Antonio Abolafio, 30, said "The worst moment was when one of them told his colleagues to put their pistols against the temples of five employees and customers and pull the trigger if the police did not retire from the scene."

Another released hostage quoted a gunman as saying, "Tell your friend [Premier] Calvo-Sotelo that he has 70 hours to decide, and if not, we are going to kill everyone, one by one," Reuter reported.

Some Tejero supporters gathered near the bank yesterday, shouting their support. Other small groups called Tejero a traitor, The AP reported.