CHRISTOPHER MARQUIS And LOURDES FERNANDEZ Herald Staff Writers

A small bomb exploded Thursday morning outside the home of a college professor who organized a controversial conference on the future of U.S.-Cuba relations, prompting cancellation of the event by the management of the hotel where it was to be held.

But the debate, entitled USA-Cuba, Another Perestroika? was immediately rescheduled for later Thursday at the University of Miami.

A man who said he was a member of Alianza de la Intransigencia Cubana -- Alliance of Uncompromising Cubans -- claimed the group was responsible for the 3 a.m. blast at the Coral Gables home of Maria Cristina Herrera, a professor at Miami-Dade Community College, who heads the Institute of Cuban Studies.

In an early-morning call to WQBA-AM radio station, the man said the group had planted the bomb at Herrera's home and would take similar action within the next 72 hours against Immigration and Naturalization Service District Director Perry Rivkind if anti-Castro militant Orlando Bosch is not released.

Rivkind, who was notified by the FBI, said security at his office was beefed up. He said he was not concerned. "I'm here working," he said. "I haven't thought about it."

Half an hour after the call at WQBA, radio station news director Tomas Garcia Fuste went on the air to condemn the bombing. Immediately afterward, the station received another call. The caller said a bomb had been placed under Fuste's car in the radio station parking lot.

The station, at 2828 Coral Way, was evacuated and a drug- sniffing police dog brought in. Police searched for two hours, but found nothing, said Miami police spokesman Ray Lang.

Freddy Yuen, an officer with the Miami police bomb squad, said this was the first time they had heard of the Alliance.

The explosion at Herrera's home did not injure any of the sleeping residents, which included Herrera, 53, her mother Maria, 79, and a house guest Luis Perez, 32. The explosion damaged a garage door and a corner of the house, and blew out the windows of a rental car parked in the driveway.

Hours earlier, a group of panelists and organizers involved in the conference met in Herrera's house and decided to exclude Elizardo Sanchez Santacruz from the meeting. The human rights activist, widely known as an internal critic of the Castro government, arrived unexpectedly in Miami Wednesday with a 90- day visa for a family reunion. Some exiles view Sanchez's visit with suspicion and have charged that he is being used by the Cuban government to clean up a sullied human rights record.

The bombing was the second in four weeks to highlight a raging debate among Miami exiles over apparent moves toward rapprochement between the United States and Cuba. On May 3, a pipe bomb shattered the glass front door of the Cuban Museum of Arts and Culture, which has been embroiled in controversy over whether to show or sell works by artists who have not broken with the Castro regime.

Bill Ripple, general manager of the Sheraton-Brickell Point Hotel, said he decided to cancel the forum Thursday morning in light of the bombing.

"I guess it was the events over the last couple of weeks and then the event at Mrs. Herrera's home," he said. "We were concerned for the safety of our guests and employees."

Ripple said he consulted the hotel's attorneys before canceling the event. He said the hotel had received no threats. "Everything was go until the bomb," he said. The hotel had hired extra police protection in preparing for the event.

A noon rally scheduled to protest the conference in nearby Brickell Park failed to materialize.

Herrera said she remained determined to host the conference after the attack.

"This was only to intimidate," she said. "If they had wanted to hurt me, they would have thrown it through my bedroom window."

The bomb was a "relatively small explosive device," said Coral Gables police Sgt. Dennis Koronkiewicz.

FBI spokesman Dennis Erich said the agency is investigating.