Terrorist bombs killed one person and injured six today, and threats of more explosions forced the evacuation of as many as 100,000 workers from Manhattan offices.

Police and firefighting squads raced to the scene as people poured into the streets from the threatened buildings in a steady rainfall, reducing all normal traffic to chaos.

Two bombs actually went off. The first was on the 21st floor of 342 Madison Ave., housing U.S. Defense Department security personnel.

An employee noticed a handbags left on a windowsill and opened it. Inside was a clock-like device. He alerted 50 co-workers to flee the office. The bomb exploded 12 seconds later, blasting the office doors off their hinges. No one was hurt.

An hour later a bomb blew out street-level windows of the Mobile Building at 150 E. 42d St., less than one block from Grand Central Terminal and on one of the busiest thoroughfares in Manhattan.

Charles Steinberg, 26, partner in an employment agency in the building, was killed. Others stumbled out, covered with blood. Shards of glass flew across 42d Street. Almost instantly, hundreds of curious passersby materialized on the scene. Large numbers of police were called in to keep them back while a search was made for further explosive.

Responsibility for the violence was taken by FALN, a Puerto Rican self-styled independence movement that has planted bombs, mainly in New York, over the past three years to dramatize its goals.

Although bombs exploded at only two sides in midtown Manhattan, the group warned of bombings at as many as 13 buildings, including the Empire State Building and the World Trade Center in lower Manhattan.

At the World Trade Center, it took two hours for 40,000 persons to leave the twin, 110-story towers. The evacuation there haulted futures trading for the day at the four commodity exchanges - New York Mercantile Exchange New York Cotton Exchange, Commodity Exchange Inc. and the New York Coffee and Sugar Exchange. A message about the bombings, said they were "just a warning" of worse destruction to come if FALN demands are ignored.

Mayor Abraham Beame repeated his demands for a capital punishment law for terrorism. He also conceded that the bombings and the threats had seriously taxed his police department, already under a severe manpower strain in the hunt for the slayer of six persons who had become known as the Son of Sam or the 44-caliber killer.

As word of the bombings spread a rash of crank calls broke out. In Brooklyn alone, more than 80 such calls were recorded, police had to check on each one. Three public buildings there were evacuated after the calls.

Fuerzas Armadas De Liberacion Nacional Puertoriquena (the Puerto Rican National Liberation Armed Forces) has claimed responsibility for 61 bombings in the U.S., 51 of them in New York City.

One such blast caused damage at the State Department in Washington on Oct. 27, 1975. Serious bombings have also occured in Newark and Chicago. Five persons have been killed and scores injured.

But despite grand jury investigation, manhunts by federal and local authorities and a standing reward of $50,000 for information, no known member of the organization has been arrested.

Nearly three full years after the first bombing, police have little more than an inkling of how large FALN is, where it is headquartered or how it originated.

After a bombing two years ago in New York, where nearly 1 million Puerto Ricans live, the police department and FBI said FALN had operations "both in New York and Puerto Rico" with a "fairly large" number of members, "perhaps as many as 100." But law enforcement agencies said they had "no idea" who heads the group.

But last fall Rafael Hernandez Colon, then governor of Puerto Rico, said FALN was estimated to have only 10 members - all on the mainland, organized in cells in New York, Chicago and Washington.

Police at that time said they by far authorities are seeking only one known suspect, 25-year-old Carlos Albert Torres of Chicago. Torres is wanted in connection with the deadiest bombing, the blast that heavily damaged the landmark Fraunces Tavern in lower Manhattan on Ja. 24, 1975, killing four persons and injuring [TEXT OMITTED FROM SOURCE]

The reasons for the bombings seem to fluctuate. Almost all of the communiques left by the FALN after their attacks contain a demand for independence for Puerto Rico.

[TEXT OMITTED FROM SOURCE] lieved no more than five or six people were involed in the bombings. Thus [TEXT OMITTED FROM SOURCE]