Dozens of crank bomb threats bedeviled police and led to the evacuation of several buildings today in the aftermath of two terrorist bombings that 24 hours earlier claimed one life and injured seven persons.

Among skyscrapers emptied was the 44-story Gulf & Western building on Columbus Circle. No explosives were found in any of the buildings.

As the FBI focused a national hunt for the bombers in the New York metropolitan area, a police raid on a Bronx apartment led to the arrest of a 27-year-old Puerto Rican, David Perez.

The Puerto Rican FALN - a Spanish acronym for Armed Forces of National Liberation - claimed responsibility for the bombs that went off Wednesday morning in a 21st-floor Defense Department office in a Madison Avenue skyscrapper and on the first floor of the Mobil Oil Building on East 42d Street. The death and injuries were incurred in the Mobil blast.

Perez, who was arrested Wednesday night after an informant's tip, was being held on charges of illegal possession of a shotgun, a revolver and about 100 rounds of ammunition.

Police Commissioner Michael Codd said that pro-FALN literature was found in his apartment and that any link to the FALN "is still under investigation."

Perez roommate, Vincent Alba, 26, was also being sought.

Three typewriters in their apartment were seized and were being examined to determine if any of them had been used to type manifestos that the FALM customarily issues following a bombing, Codd said.

An FALN note left in Central Park after the blasts Wednesday was similar to previous communiques. It demanded independence from the United States for Puerto Ricans and other minorities and the release of five Puerto Rican terrorists jailed more than 20 years ago for trying to kill President Truman and five U. S. congressmen.

Law enforcement authorities so far have been unable to crack the FALN, which has claimed responsibility for more than 50 bombings in the last years in New York, Newark, Chicago and Washington. Most of the bombings have been aimed against banks and corporations, which, the FALN says, "strangle us with their colonial yoke."

Grand jury investigations into the FALN are under way here and in Chicago. Three persons are in jail for refusing to testify about the group's activities.

But investigations so far apparently have been fruitless. As an FBI spokesman in Chicago said: "How can you even find out who is in the FALN? It's very difficult to investigate a terrrorist group performing criminal acts . . . Witnesses are almost impossible to develop because of you have a very small, dedicated organization that is loyal."

A member of the New York Police Department's Arson Explosion Squad, which has worked for two years on the FALN bombing of Fraunces Tavern - which killed four persons and injured 53 in January, 1975 - said: "We're dealing with a highly intelligent group. They're not the kind of people who go around bragging in bars."

If they have slipped up, he said, "We haven't found it."

Police said the FALN may have about a dozen members. One theory is that the group is broken down into separate units, with identities carefully shielded from the others.

Although the FALN claims to speak for Puerto Rican advocates of independence, the group is not known to have significant contacts or a following in Puerto Rico.

Authorities there are convinced that the cell consist of "Newyoricans," New Yorkers of Puerto Rican origin. New Yoricans are often received with less than open arms in Puerto Rico when they return to take up residence or to visit.

Of the 5 million Puerto Ricans only 3 million live in Puerto Rico with the remaining 2 million on the mainland, most of them in New York.

Generally, a culture gap has developed. Many Newyoricans no longer speak Spanish well but have not yet mastered English. Sometimes they are misfits in both countries.

Most of the violence over the years in the name of Puerto Rican independence has been committed on the American mainland and in many case the persons responsible have had little contact with the island.

The two most spectacular act of Puerto Rican nationalists - the 1950 assassination attempt on President Truman and the 1954 attack on Congress were committed in the continental United States by New York residents of Puerto Rican origin.