Former Washington lobbyist Fred B. Black Jr. and three other defendants were convicted here yesterday by a U.S. District Court jury for their roles in what prosecutors called a "complex, sophisticated and lucrative" cocaine trafficking and money laundering ring between 1977 and 1982.

The jurors deliberated for 2 1/2 days before ending the eight-week trial with guilty verdicts against Black; John C. Tarantino, a New Jersey lawyer; Wilfred Samuel Bell, of Annapolis, and Robert H. Burns, a Miami attorney.

District Judge Thomas F. Hogan ordered Bell, who was extradited from England, jailed immediately pending sentencing. Burns is serving a prison sentence in an unrelated case. Black and Tarantino were freed on bond.

The four were charged in December 1983 with conspiracy and a variety of other drug-related offenses in an action hailed by the Reagan administration as the first indictment returned in connection with its Organized Crime Drug Enforcement Task Force.

"It's a superb verdict in a very significant case," U.S. Attorney Joseph E. diGenova said yesterday. "It underscores the ability of the federal government to reach trans-national cocaine trafficking operators and secure convictions."

Marcos Cadavid, one of the ring's alleged Colombian suppliers, was extradited from that country in January, and his trial is scheduled to start here on Monday. Tarantino, the assistant city attorney in East Orange, N.J., appeared stunned yesterday as he walked silently from the courtroom.

"Well, I'm sorry we got clobbered," Black told him. "Keep your chin up."

Tarantino was convicted of conspiracy and four counts of illegal in- terstate travel in connection with the ring's activities and faces a maximum sentence of 35 years in prison and a $65,000 fine.

He was acquitted of possession of cocaine with intent to distribute.

Prosecutors alleged that the four men were part of a drug ring run by Lawrence G. Strickland Jr. of Bethesda that bought dozens of kilograms of cocaine through a Miami connection with Colombian drug smugglers and reaped millions of dollars in profits.

The drugs were distributed in the District, Texas, California, New Jersey and elsewhere, the government charged.

Bell, who lived near Dupont Circle at the time, was described in court as "the biggest outlet for Strickland's cocaine in the Washington area."

Prosecution witnesses testified that the cocaine was purchased for between $49,000 and $60,000 per kilogram and resold for $100,000 per kilogram or more.

The operation generated suitcases full of cash that Strickland funneled to Black for laundering through two disguised accounts at the Riggs National Bank branch at the Watergate, where Black lives, according to prosecutors.

Strickland, who pleaded guilty earlier, was the government's star witness.

According to Strickland's testimony, Black laundered almost $1.5 million through the Riggs branch, sometimes making several deposits in a day in order to break the total into smaller amounts.

The branch was managed at the time by Riggs vice president William G. Hessler, whose wife is Strickland's sister. Hessler and Black face trial this month in U.S. District Court on separate charges related to the alleged laundering activities.

Black, a once-prominent Washington lobbyist and business associate of former Senate aide Robert G. (Bobby) Baker, denied on the witness stand that he knew that Strickland was a drug dealer.

Judge Hogan did not immediately set a sentencing date.

Black faces a maximum penalty of 20 years in prison and a $35,000 fine; Bell 30 years and $50,000, and Burns 15 years and $25,000.