A private investigator testified yesterday that he passed along $500 in bribes to a D.C. police officer to help a client -- a suspected drug dealer -- get back a truck that had been seized by police.

Clement F. Brown testified in U.S. District Court in Washington as the government's star witness in the trial of Wallace S. Najiy II, a former vice officer in the 4th Police District who is accused of conspiracy, bribery and other charges. Najiy, 36, resigned after his indictment in January, ending an 11-year career.

Since its start last week, the trial has provided an unseemly picture of courthouse life. Brown, 63, a longtime criminal defense investigator, got to know Najiy and other D.C. police officers by playing cards with them in an office at D.C. Superior Court. He said he spent every working day at the courthouse and touted his police connections to attract clients. On his business card, Brown promoted himself as an investigator, process server and paralegal. He acknowledged in court that he had no paralegal credentials.

The charges against Najiy stem from his arrest in September 1995 of Gregory D. White on Georgia Avenue NW. After finding cocaine in White's 1987 Dodge Raider truck, Najiy seized the drugs and vehicle. The truck was to be held in a police impound lot for possible forfeiture proceedings.

White, now 39, testified last week that he met Brown a day after the arrest, shortly after his first court appearance. According to White, Brown told him that he knew Najiy and that he could get matters "squared away" for money. White said he subsequently gave Brown three checks totaling $2,800, which he believed would lead to the return of his truck. He said he got back the vehicle, along with a ring that was taken from him during the arrest.

White pleaded guilty in D.C. Superior Court to a charge of possession with intent to distribute cocaine. He was given probation, which he completed, and now works as a chauffeur in Maryland. He was not charged with any crimes involving the alleged payments.

Brown, however, was indicted along with Najiy. He pleaded guilty in March to one count of aiding and abetting in the bribery of a public official and agreed to aid the prosecution. In return, nine charges against him were dropped. Brown could receive probation at his sentencing, which was delayed so that prosecutors and Judge Thomas F. Hogan can evaluate his cooperation.

During his testimony yesterday, Brown said Najiy raised the subject of money when Brown asked him about releasing White's truck. He quoted the officer as asking, "What's he working with?" and said Najiy didn't back down even after being told that White and his family didn't have much money. He maintained that he gave Najiy the $500 in two installments of $250 each. Najiy, he said, took the cash each time without any comment.

Brown said he couldn't recall how much money he kept for himself. He said he forwarded money to White's defense attorney, too.

Najiy's attorney, Michele Roberts, told jurors in opening statements last week that Najiy took no money and did nothing wrong. She described Brown as a "two-bit hustler" and said he convinced Najiy that White's family desperately needed the truck to transport children. According to Roberts, Najiy acted out of goodwill in getting the truck released, knowing that the police department has little use for a vehicle "with well over 100,000 miles on it."

Roberts said White only assumed Najiy was getting paid because that's what Brown told him. "Wallace Najiy did not accept any bribes," she said, contending that Brown was making up a story to keep himself out of prison.