The Fairfax County Board of Supervisors, spurred by last week's death of a construction worker in a job-site cave-in, voted unanimously yesterday to sue federal and Virginia safety agencies it said are conducting inadequate safety inspections.

"A cruel hoax is being perpetrated on the workers of Northern Virginia," said Supervisor Alan H. Magazine (D-Mason) during the boards's 90-minute debate. "They go into construction sites believing that the government is protecting their lives, but in fact that isn't happening."

In a separate action, board members also ordered county inspectors to begin spot checks of building sites in the county and shut down those in which extensive violations of federal job safety rules are detected.

County officials said the task force will meet with chief prosecutor Robert F. Horan Jr. to seek prosecution of construction companies found to be in consistent violation of job safety standards.

The board's action comes amid a lengthy dispute between county, state and federal agencies over allegedly insufficient inspections and the legal right of Fairfax to use its own inspectors.

The suit, which county officials said would be filed within a week in federal court in Alexandria, would be aimed at winning permission for Fairfax to use county-employed inspectors on construction sites.

The task now is carried out by state officials, with three full-time inspectors assigned to Northern Virginia -- a number repeatedly criticized by board members yesterday as too few.

Supervisor Audrey Moore (D-Annandale) called the inspection situation in Northern Virginia "disgraceful" and said of the board, "We've been inept and have not done our job."

Milton V. Peterson, a major builder in Fairfax, said he couldn't comment on the supervisor's action until he studied it more closely, but added: "The general awareness of safety now as opposed to 10 or 15 years ago has improved tremendously. I don't think that the recent tragedies prove that standards are not being enforced. Some accidents will happen."

Peterson, one of the partners in the development of the new town of Burke Centre, said efforts to save trees and other such environmental controls can sometimes increase safety problems.

"I'm not opposed to such controls," he said, "but this is one of the results you can get." He explained that builders, in trying to save trees sometimes are forced to dig narrower and steeper trenches during excavation work.

The federal government, which has ultimate responsibility for worker safety in Virginia, has allowed the state to conduct its own inspection program, subject to federal review. Virginia was originally slated to receive federal approval for its program last month but federal officials yesterday refused to predict when or if approval would be granted.

"It's fair to say we still have a number of concerns that need to be resolved," said Grover Wrenn of the federal Occupational Safety and Health Administration.

State officials say neither state nor federal regulations allow for the type of local enforcement Fairfax County has suggested.

"If we told the county to go ahead and do it, it would be just as though we told the Marines to invade China," said Robert Beard, Virginia's commissioner of labor and industry. "We simply don't have the power to tell them to do it.

"It's conceivable they could be liable for damages" in the cases of builders who incurred financial losses as a result of county-ordered work stoppages, Beard said.

Acting County Executive J. Hamilton Lambert declined yesterday to discuss the county's legal right to shut down unsafe job sites. "I don't care who does the work as long as it is done and adequately done," Lambert said. "This is a question of a high level of frustration."

Last wee's cave-in death was the 14th construction-related fatality in Northern Virginia in the last two years. The latest victim, George Cooper of Harpers Ferry, W.Va., died after an unsupported, 16-foot-deep trench in which he was laying sewer pipe at a West Springfield site collapsed. A second worker, buried up to his shoulders in dirt, broke an ankle.

The men's employer, the William B. Hopke Construction Co. of Alexandria, had been cited by inspectors one month earlier for shoring violations, according to state officials.

Earlier this month, a federal task force from the Occupational Safety and Health Administration, following up complaints of inadequate safety inspections, cited local contractors for 160 safety violations at nonresidential building sites.

Residential building sites are currently checked by the three state inspectors assigned to Northern Virginia, plus a team of six federal inspectors sent here pending U.S. approval of the state safety program.

County officials have conceded that they do not know exactly how many inspectors are necessary to guarantee the safety of construction workers -- a point emphasized by one state official yesterday.

"Federal authorities had a task force out there [in Northern Virginia] for a whole week and that fellow in Springfield still died," said Beard, who heads the state's OSHA program. "Unless you have two inspectors for every site, you're going to have fatalities."

In an opinion last spring, Virginia Attorney General J. Marshall Coleman said Virginia's safety enforcement plan precludes local authorities from issuing stop-work orders to violators of occupational safety standards. Coleman suggested instead that local authorities either forward reports to state inspectors or seek legislation to amend the state plan.

Coleman, through an aide yesterday, declined to comment on the legal prospects of actions the Fairfax task force may take. "I suspect the courts will have to settle it," Toni Radler, Coleman's spokeswoman, said.

During yesterday's debate, Fairfax board members discovered that a letter from the county calling for the U.S. Labor Department to reject the Virginia OSHA plan as a "failure" wasn't signed and mailed until Nov. 8 -- two months after the supervisors ordered it sent.

Board Chairman John F. Herrity disclosed during the debate that he declined to sign a draft dated Oct. 15 and sent it back to the county attorney's office for revision. The letter finally went out over the signature of the acting county executive.

"The draft was too long," Herrity said. "There aren't any other reasons."