Two airplanes belonging to the Cuban government were damaged by explosives while they were being serviced at Miami International Airport in August, 1959.

Presumably the bombers were enemies of Cuban Premier Fidel Castro, who was deprived of his airplanes.

On the night of March 31, 1963, someone placed a bomb outside the apartment door of Luis Balbuene Calcadilla. He was not there, but his wife and infant daughter narrowly escaped injury and the apartment was wrecked.

Balbuene, then living at 908 SW 5^th Avenue, blamed the attack on Castro agents.

Authorities remember the two incidents because they marked the beginning of the terror blamed on some Cuban exiles in Miami. The airport bombing was the first in Dade County attributed to Cubans, and that at Balbuene's apartment was the first in Miami.

The total now stands at 53 - 29 in Miami and 24 elsewhere in the county.

As it has from the beginning, the terrorism seems to spring from different causes. Some bombings apparently are intended to further one cause or another. Others are for the financial benefit of the bombers.

Lt. Harvard Swilley, chief of the Miami Police intelligence unit, said:

"In my opinion, these Cuban bombings can be divided about 50-50; half are political and half are for extortion."

Swilley and Capt. Thomas Brodie, chief of the Metro Bomb Squad, agreed that the bombers also mix politics and profit.

"They give an air of legitimacy to what they're doing by bombing a Mexican airline office, a Polish freighter or a consulate, proclaiming that it is because those nations deal with Castro," Swilley said.

"Then they go to a merchant and demand that he help finance the cause. If he refuses to be shaken down they bomb his place of business."

The number of bombings blamed on the Cubans has increased sharply this year. There had been 13 in the city and county up until the first of this year; 40 have been counted in this year, which began with a blast last January in the car of a jeweler.

Swilley said police don't automatically look for a Cuban exile every time a bomb goes off. Out of 34 under investigation, he said, 24 were believed to be the work of Cubans while the other 10 were blamed on the underworld and on a couple of amateurs attempting murder.

Miami police said seven of 15 persons arrested in bombing cases were Cubans. The sheriff's office made two arrests - both of Cubans - for bombings.

The job of fixing the blame for the bombings (or giving credit, as some of the Cubans put it) is complicated by the proliferation of anti-Castro groups. There are about 50 in Miami. Two of them call themselves Poder Cubano, or Cuban Power.

The bombings of consulates have become so frequent that five representatives of foreign governments threatened last month to move their offices out of Miami if they were not protected.

Miami authorities promised to put a police watch on the offices. The Coast Guard and police, meanwhile, added guards at the Dodge Island port.