In a dark blue windbreaker and light blue slacks, Fred B. Black Jr. looked like a visitor from the country in federal court here yesterday.

But U.S. District Judge Thomas F. Hogan described the 70-year-old former lobbyist who lives in the Watergate Apartments as a "sophisticated, intelligent man-about-Washington."

Assistant U.S. Attorney Roger Adelman called Black a "morally bankrupt . . . perpetual criminal" and said he was "an architect" of a conspiracy to establish a nationwide cocaine distribution ring and launder millions of dollars from cocaine sales.

After the statements, Hogan sentenced Black to seven years in prison on the narcotics conspiracy conviction and fined him a total of $40,000.

"Whether through greed or to make your one big score in life, you have led a very fine life for at least 10 years with no visible means of support," Hogan told Black.

In March, after a two-month trial, Black and three other defendants were convicted of conspiracy to import and distribute cocaine. After a second trial, Black was convicted last month on three counts of income tax evasion involving $473,000 in unreported income in 1978, 1979 and 1981.

Yesterday Hogan also sentenced Black to five years in prison on each of the tax counts and to three years' imprisonment on a charge of interstate travel to carry on unlawful activity, of which Black was convicted at the first trial. The judge said the prison sentences are to be served concurrently.

Prosecutors said that Black could be expected to spend at least six years in prison before becoming eligible for parole.

Black's attorney, Thomas Dyson, who described Black as a "good man" who "was not in the narcotics business," said Black will appeal and asked that he remain free on bond. But Hogan ordered Black to report to prison as soon as federal officials tell him where he is assigned to go.

Dyson said Black is now indigent. In a courthouse hallway later, Black said his rent at the Watergate already is "four months past due."

During the 1960s, Black was a business associate of former Senate aide Robert G. (Bobby) Baker, and a well-known Washington figure. Black was convicted of income tax evasion in 1964 but was acquitted in a retrial after the Justice Department disclosed it had illegally placed a microphone in his apartment. Later he was awarded $903,000 in damages, but the award was set aside on appeal.

The key witness in Black's recent trials was Lawrence G. Strickland Jr., who said he brought about $1.5 million in cash to Black in his Watergate apartment for deposit in bank accounts that Black controlled.

Strickland, 34, who grew up in Northwest Washington, was described by prosecutors as the leader of the cocaine ring. He has pleaded guilty to several drug and tax charges and is awaiting sentencing.

Black testified that he did not know that any of the people he dealt with were involved in drugs and said he believed all the cash came from legitimate sources.

Yesterday Hogan noted that Strickland brought large sums of cash to Black while wearing blue jeans and a T-shirt and had testified without contradiction that he once pulled thousands of dollars out of a boot which Black then put into a freezer for safekeeping.

"It's beyond imagination that you did not realize that some part of these funds came from narcotics," Hogan declared. "Businessmen simply don't do business this way."