A Virginia judge yesterday dismissed for lack of evidence the first court case arising out of a year-long investigation of alleged payoffs to building inspectors in fast-growing Prince William County.

"You're wasting your time," General District Court Judge William R. Murphy told a defense lawyer who had risen to make his final argument in yesterday's preliminary hearing of the bribery case of Manassas plumbing contractor Luther Anderson, 43. Murphy then dismissed the charge against Anderson.

The prosecution's case faltered at after the key witness county plumbing inspector Eugene Raymond Bradley, failed on the witness stand to identify Anderson as the contractor who allegedly offered him a payoff to overlook incomplete construction work.

"There's no probable cause to send this case to the grand jury based on the evidence I've heard here this morning8" Murphy told prosecutors.

Anderson was one of five Northern Virginia contractors charged with bribery as a result of the probe. The investigation by county and Virginia Department of Commerce officials followed a large number of complaints from home owners about shoddy construction and allegedly broken promises by contractors.

Yesterday's dismissal was the latest in several unsuccessful attempts to prosecute Prince William builders in recent years. One top county official has called such attempts "a legal nightmare" because of the complexity of Virginia's building laws.

Prosecutors also had difficulty proving yesterday that the cash allegedly offered to Bradley was a bribe.

Bradley testified that he made a special trip to the Greenwood Farms town house development, a subdivision near Dale City, after receiving a phone call from a man who identified himself as Anderson. Bradley said he had not met Anderson before.

When he told the man he could not approve the plumbing work, Bradley testified the man took out cash and said: I'd like you to have this."

Bradley said he refused the money. He said he did not report the incident until months later after county police announced the investigation.

He said under oath yesterday that builders frequently offer inspectors gifts for making special trips, like the one he made in this case to inspect sites.

"I cannot say whether Mr. Anderson was trying to bribe me or whether he was trying to be nice to me," Bradley testified.

When the judge at one point interrupted the questioning and asked Bradley if Anderson was the man who offered him the money, Bradley replied: He looks like the man."

Dissatisfied with Bradley's reply, the judge persisted: "Is this the man? Yes or no, that's the issue."

"Your honor," Bradley said, "I cannot be absolutely certain about that. I do not know."

Bradley said he also did not recall the date when the alleged offer was made. The prosecutor said it took place on July 15, 1979.

Investigator David Lagervild, who has conducted the probe along with state investigtors, testified that when he arrested Anderson, Anderson acknowledged meeting with Bradley but denied offering him any money.

Under Virginia bribery laws, the prosecution does not have to show an actual exchange of money, but only that builder attempted to influence an inspector by offering him money.

Prosecutors could reinstate the bribery charge against Anderson by taking the case to a grand jury, but they said no decision has been made yet.

Investigators vowed the probe will continue.

On Monday, a grand jury returned two bribery and three false pretense charges against Stephen J. Siegel, whose controversial development of homes in the Montclair Country Club Lake subdivision triggered the probe.

Siegel, who moved to Florida after his company, Tray-Marc Construction Co. of Dumfries, lost its state contractor's license, is accused of offering two payoffs to former county building inspector Charles J. Wright, who resigned after the probe began, reportedly is cooperating with investigators and is expected to testify against Seigel and other builders.