A Dutch prostitute told a federal court jury here yesterday how she befriended an American man she met in Amsterdam so she could get to the Untied States and then found out he was smuggling heroin back to Washington.

Nicolette Wempe, who worked at a legalized prostitution house called the Jap Jum Club, said that although she spent several weeks with Ernest Minder in Amsterdam and the United States in late 1976, it wasn't until early 1977 that she realized why Minder was making trips to the Netherlands.

Wempe, 25, said that after a 5 a.m. telephone caller summoned Minder to a house in an old section of Armsterdam, he returned to her apartment. She said, "He unpacked a bag. In that bag was heroin, gray little rocks."

"I said, "This must be heroin or I am crazy.' He looked at me like I was crazy," she recalle as the jury and others in the courtroom laughed at her testimony.

Wempe went on to describe how Minder, who was found shot to death in his white Cadillac in Southeast Washington last October, meticulously cut up the heroin into small amounts. She said he tne carefully sliced open hardpack boxes of Marlboro cigarettes, dumped out the cigarettes, placed the heroin back into the empty boxes and glued the containers shut.

"I asked him how much all this was worht," she recounted in a lilting voice." He said, 'About $60,000.'"

Wempe was testifying in the heroin importation conspiracy trial of alleged Washington drug Kingpin Linwood Gray and 11 codefendants. Her testimony was the first the eightwoman, four-man jury has heard about how the heroin was actually stuffed into the cigarette boxes for transporting to this country.

According to earlier testimony in the case, the heroin-filled Marlboro cartons were then substituted for duty-free cigarettes purchased at airports in Copenhagen and Amsterdam and toted back into the U.S. in shopping bags.

Federal investigators charge that the ring allegedly headed by Gray imported $30 million worth of extremely high grade heroin from Amsterdam, through Montreal and Chicago, to the streets of Washington.

Wempe said that at first Minder gave her money for clothes, bought her transatlantic airplane tickets to visit the United States and took her to horse races at Laurel and Bowie and in New York. But she said that after she learned Minder was running heroin to the United States, she decided she "didn't want to have anything to do him or his friends anymore."

The jury earlier heard testimony from Rene Clark, 25, who told the jury that one of Gray's alleged lieutenants, Robert L. Stuckey, recruited her to help ferry heroin from Amsterdam to Washington.

When she returned to this country, Clarke said, she was arrested by customs officers at O'Hare International Airport in Chicago because she had a "Thai Stick" in her wallet - a marijuana cigarette dipped in opium. She said she fined $25 by customs officials and chastised by Stuckey, who had told her to get rid of any personal drugs before traveling back to the United States.