An investigation into allegations that housing developers paid off building inspectors in fast growing Prince William County is expected to lead to a series of arrests, perhaps by week's end, police said yesterday.

Police investigator David Lagerveld said yesterday that the three-month probe, which originally focused on one developer, Tray-Marc Construction Co. of Dumfries, has since been expanded to include accusations against several other builders. He would not state a specific number.

Edward G. Andres of the Virginia Department of Commerce, which has assigned two investigators to the case, said at least six state-licensed contractors are under investigation.

Neither man would reveal the names of the companies or inspectors being investigated. But officials have said Tray-Marc president Stephen J. Siegel, at one time one of the country's largest builders, is one of those under scrutiny.

Siegel, who reportedly moved to Florida earlier this year after more than a dozen complaints surfaced about shoddy workmanship in houses he built in the affluent Montclair Country Club Lake area, could not be reached for comment.

The complaint led to a Commerce Department hearing in July that held Tray-Marc guilty of "gross negligence, continued incompetence and misconduct as a general contractor," and "willful failure to comply with the Virginia Uniform Statewide Building Code."

A hearing officer ordered that the firm be stripped of its state license to do business as a contractor -- the first time in at least five years such an action has been taken, according to Andres.

Andres said yesterday that if allegations against other builders are substantiated, the other firms could face similar action.

It was while examinig complaints from homeowners about Tray-Marc that state investigators came upon accusations that building inspector had falsified records and taken bribes to cover up for the builder.

Lagerveld said county records showed at least one building inspector approved a house foundation that was never laid and that an approved basement was merely a hole in the ground. He also said records showed at least five instances where inspectors approved work that had never actually been done.

One building inspector, who has not been named, was placed on administrative leave for four days in August because of allegations against him. He later returned to work but has not been allowed to conduct inspections alone.

Lagerveld yesterday would say only that he was investigating allegations against more than one inspector.

"We have a real problem proving bribery in a case like this," said Lagerveld. "The building inspector comes to work in the morning, picks up a group of white cards and goes out alone checking work all day. If he takes a payoff sometime during the day, nobody knows it except him and whoever gave him the money."

"Right now, we've got a lot of innuendo and a lot of hearsay, but we're still looking to verify the charges," said Lagerveld, who predicted the criminal investigation would take at leaast another two weeks.

County Construction Service chief Charles Vincent, said his inspectors have had trouble doing their work because of the investigation.

"There's a lot of pressure right now," said Vincent. "People are afraid that if they make a mistake on an inspection, they'll be considered a suspect. I just hope they wrap this thing up quickely."

The inspectors, whose annual salaries range from $11,000 to $19,000, have been confronted with an increasingly complex job in recent years as the county has grown from a secluded rural area to a booming bedroom community. tThe county issued 1,812 residential building permits last year -- more than double the 741 permits issued in 1975.

Home buyer complaints about shoddy construction and broken promises from builders have also soared -- up 50 percent in the last year, according to the county's Office of Consumer Affairs.