According to his lawyer, William G. Hessler was a "very trusting . . . gentleman banker" when he managed the Watergate branch of the Riggs National Bank.

"Mr. Hessler didn't like details," lawyer John A. Shorter told a jury yesterday at U.S. District Court in Washington. "Mr. Hessler didn't like paper work . . . [and] Mr. Hessler was conned."

According to federal prosecutors, the situation at the bank branch from 1978 to 1982 was quite different. Assistant U.S. Attorney Roger M. Adelman said Hessler was part of a conspiracy to launder more than $1 million from cocaine sales, accepting suitcases filled with cash, taking $40,000 in bribes and making fraudulent loans on which the bank lost $130,000.

"Mr. Hessler created false records and false documents," Adelman said, and he "in effect gave [away] " Riggs' money.

These two portraits of the 47-year-old former banker, who most recently was employed as a house painter, were presented in opening arguments yesterday as Hessler went on trial with former Washington lobbyist Fred B. Black Jr., 70.

The two men are accused in a 53-count indictment of racketeering, mail fraud and income tax evasion as part of a scheme to launder the money earned by a major cocaine distribution ring that smuggled the drug from Colombia and sold it in many parts of the United States.

Lawrence G. Strickland Jr., 34, the third man named in the indictment, has pleaded guilty to the charges and will testify against the other two, Adelman said. Prosecutors have described Strickland, who grew up in Northwest and lives in Bethesda, as the ringleader.

Last month Black and three other men, including attorneys from New Jersey and Miami, were convicted here of conspiracy to import and distribute cocaine. Marcos Cadavid, an accused Colombian cocaine wholesaler, was convicted of conspiracy in a separate trial.

During the 1960s, Black was a well-known Washington figure as a business associate of former Senate aide Robert G. (Bobby) Baker. He was convicted of income tax evasion in 1964 but was acquitted in a retrial after the Justice Department disclosed that it had illegally placed a microphone in his apartment.

Yesterday Adelman said Black received the drug money from Strickland, who is a brother of Hessler's wife, and that Black deposited it in accounts he controlled for two companies that were just "shells" for racketeering. He said Black "kited" checks and failed to pay income taxes from 1978 to 1982 even though he lived in an expensive apartment in the Watergate and had personal expenditures of $538,000.

Both men pleaded not guilty to the charges now being tried, on which each faces a maximum penalty of more than 70 years' imprisonment and $570,000 in fines.

Yesterday, Black's lawyer, Thomas Dyson, acknowledged that Black deposited large amounts of cash in the bank but said the money was used in a legitimate venture to construct a gambling casino and hotel in Atlantic City, a venture that eventually was unsuccessful.

The trial is expected to last several weeks.