When he was deputy prime minister of the Grenadian revolution, Bernard Coard was known in public as a bookish theorist of Marxist economics with a round belly and a ready chuckle.

But the man who emerges from the minutes of the revolution's Central Committee meetings as a second in command who was a secret manipulator whose maneuvers to push aside Prime Minister Maurice Bishop and impose a tough Marxist-Leninist line on this easy-going island produced a bloody explosion, followed by a U.S. invasion.

Now, nearly two months after his capture by U.S. soldiers, Coard is described by his visitors and jailers as unrepentant, increasingly indignant at his imprisonment without charges and angrily threatening to sue the United States and other Caribbean governments for kidnaping and libel.

Coard has outlined his plans in complaints to Caribbean Peace Force guards and Archdeacon Hoskins Huggins, an Anglican priest who ministers to the former deputy prime minister and 34 other political detainees in Richmond Hill Prison. As described by him and Lt. Col. Delroy Ormsby, the Caribbean force commander, Coard seems unbeaten by the failure of his revolution and unaware of--or at least unwilling to recognize--Grenadians' widespread hatred of him for his role in the turmoil that led to Bishop's killing on Oct. 19.

Coard's reported determination to fight his imprisonment by whatever legal and political tools he can find underlines the potential problems he poses for Governor General Paul Scoon and members of the Advisory Council who have been ruling Grenada since U.S. troops invaded the island on Oct. 25 and unseated the Revolutionary Military Council, nominally headed by Gen. Hudson Austin.

Soon after the invasion crushed all resistance on the island, U.S. soldiers captured Coard, Austin, other Revolutionary Military Council members and Coard's wife Phyllis from separate hideouts. They were kept secretly for several days aboard the nearby U.S. Navy ships Guam and Saipan, and then turned over by U.S. officials to the Richmond Hill Prison, where they have been held without charges and with restricted access to legal counsel.

Scoon originally announced they would be investigated by a British-style commission of inquiry to give a public accounting of the Oct. 19 violence. On advice from a now-departed British constitutional adviser, however, he changed his mind, citing fears that such findings could jeopardize a fair trial. Instead, the Advisory Council invited Scotland Yard detectives to help organize evidence for submission to a Grenadian director of public prosecutions, who would formally bring charges for a trial.

Council Chairman Nicholas Braithwaite earlier had expressed hope that charges could be brought by Christmas. But the director of public prosecutions has left the island for a vacation, and the matter has been put off.

Several Grenadians have expressed fears that a trial would be difficult for several reasons.

First, they say, an impartial jury would be difficult to gather since islanders seem unanimous in condemning Coard for Bishop's killing and the army decision to fire on Bishop's supporters. Braithwaite said in a recent interview, for example, that Coard clearly was "the power behind the throne" during the killings.

In addition, Coard formally resigned from the government several days before the Oct. 19 violence and now is arguing that he cannot be held responsible.

More broadly, some Grenadian lawyers, including opponents of the revolution, say that defense attorneys could find avenues to attack the constitutionality of Scoon's assumption of all-inclusive powers behind the force of U.S. troops and his imprisonment of Coard, Austin and the others for acts that could be defined as political as well as criminal.

But none of this has happened so far, and, in the absense of any developments, Coard reportedly is growing increasingly angry at his undetermined fate. He accuses U.S. troops of kidnaping him and libeling him by publishing his photograph with Austin's and another revolutionary leader's on a post-invasion propaganda poster denouncing them as bloody tyrants.

Archdeacon Huggins said that Coard has spoken of plans to sue the United States and governments of seven Caribbean nations that participated in the invasion for the alleged kidnaping and libel, and to sue U.S. and other newspapers for their reporting on the crisis. Ormbsy said Coard has mentioned the sum of $50 million in discussing the threatened suits.

Coard also expressed anger at Ormsby's refusal to allow a visit by a U.S. congressional Black Caucus delegation last week. Former U.S. Attorney General Ramsey Clark, retained by Coard's family, said he was refused permission to visit his client on two trips to Grenada. But an associate, Jamaican lawyer Jacqueline Samuels-Brown, had access to Coard for the first time last week, seeing him Thursday, Friday and Saturday, Clark said.

Braithwaite said Clark was denied authorization because he had not been "called to the bar" to practice in Grenada, a necessary authorization. Samuels-Brown, trained in Caribbean law, was easily admitted, he added.

Coard's wife Phyllis, Clark said, also is having trouble getting a special diet made necessary by recent gall bladder surgery.