By PHIL GAILEY

WASHINGTON - It was a brief announcement at the State Department's regular press briefing on Aug. 21, 1969:

Lazaro Eddy Espinosa Bonet, the third secretary of the Cuban mission at the United Nations, had been asked to leave the United States for reasons related "to the security of the office of the President."

What was not revealed at the time was the diplomat's role in a bizarre Cuban plot to place then-President Nixon's vacation home at Key Biscayne under surveillance.

The plan, which called for bugging the Nixon residence and a commando raid by Cuban frogmen, was never implemented.

But its discovery gave U.S. authorities an excuse to crack down on "Superactive" Cuban intelligence agents masked as U.N. diplomats in New York, according to government sources.

THE STORY, parts of which were reported eight years ago in The Miami Herald, has surfaced again - this time in a Jack Anderson column.

The Secret Service, the FBI and Nixon's office in San Clemente all refused comment on the Anderson report Thursday.

Ron Ziegler, Nixon's former press secretary, said, "This is the first time I've ever heard of anything like that."

Bebe Rebozo, the former President's closest friend and one-time neighbor on Key Biscayne, said the same thing. "My impression is that it is more fiction than fact," Rebozo said. "If there had been any such plot - frogmen - I think the President would have transmitted the information to me."

Government sources in Washington confirmed the basic elements of the Anderson report, but emphasized that the plan was more of a surveillance scheme than anything else.

There is no evidence that Cuban commandos planned an assassination attack on Nixon, according to government and intelligence sources.

IT IS UNLIKELY, they added, that the Cubans would even have attempted to blow up the presidential compound.

"We assume their main interest was intelligence-gathering," said one source familiar with the plot. "The Cuban (intelligence) agents working out of the U.N. were superactive in those days and were concocting some wild schemes to try to prove themselves and impress their superiors."

U.S. authorities used the incident to crack down on the intelligence gathering of Cuba's diplomats at the U.N.

Shortly after Bonet's expulsion, the State Department ordered two other Cuban diplomats, Rogelio Rodriguez Lopez and Orlando Prendes Gutierrez, to leave the country for spying.

At the same time, according to government sources, it delivered a stern warning to the Cuban U.N. mission about its intelligence - gathering activities.

Why would Cuba plot such a James Bond-type scheme?

One State Department official offered this view: "You can assume that if we were as stupid as we were, trying to make Castro's beard fall out and all that, that they were equally stupid for coming up with such a wild-eyed scheme."