A D.C. police officer testified yesterday in D.C. Superior Court that a woman complained to him that another officer had her perform a sex act, instead of arresting her on a prostitution charge.

Minutes later, the policeman said officer Albert Sell pulled up in his patrol car and the woman began screaming, "That's the officer right there, that's the officer."

"I told him, 'I think you better call a sergeant from the Second District that you know real well,' " Officer Keith Brian Matthews testified during the second day of Sell's trial on sodomy, bribery and obstruction of justice charges.

Sell, who has been suspended without pay, allegedly drove the woman to a parking garage on Sept. 30, 1980, and had her perform a sex act on him.

The obstruction of justice charge stems from another incident in which he allegedly attempted to influence the woman's grand jury testimony after she filed a complaint.

During cross-examination of the woman yesterday, Sell's attorney attempted to show that she could not remember clearly many of the allegations she made about the Sept. 30 incident and that she subsequently tried to prevent other solicitation arrests by warning she was a government witness.

Attorney Robert E. Greenberg asked if she had said to other officers, "You can't mess with me, I'm a government witness."

Lois Frontuto, 33, said she had said something like that once, but she told the jury the case had made life on the street more difficult, not less. She said she subsequently was jailed on a prostitution charge and that no prosecutor helped her.

Matthews testified yesterday that Frontuto appeared disturbed as she told him about the incident with the other officer. Matthews said he radioed for a superior and Sell, who said he was the acting sergeant that night, responded.

When Matthews told Sell about the allegation, he said Sell told him to arrest Frontuto for "disorderly sex." Matthews told him he could not do that.

"If it is the truth . . . " Matthews recalled saying, "you should have locked her up" at the parking lot. "It was a felony."