When Mike and Nancy Johnson traded their small Annandale home for a five-bedroom, $100,000 house in Prince William County in the spring of 1978, they made what they now call "the biggest mistake of our lives."

Just entering their new front door was a challenge. The house had no front steps.

When it rained, the basement flooded. Sometimes the water would rise two feet above the basement floor. Three times they had to summon the fire department to pump the house dry after storms.

Finally, they carefully placed 32 sticks of dynamite in their yard and leterally blew it up in order to install a drainage system.

Today -- 19 months and $13,000 in repair bills after they moved in -- their home is still unable to pass the country's inspection.

What has happened to them is in many ways a window on the troubles currently shaking fast-growing Prince William on the southern edge of metropolitan Washington. Last week county officials announced they were charging five home builders -- including the man who built the Johnsons' home -- with bribing a former county inspector to approve shoddy home construction.

The scandal and the trials it is expected to bring illustrate the troubles a rural county can encounter as it attempts to cope with rapid-urbanization and, at the same time, maintain the low-profile, pro-business type of government Virginia long has preferred.

The Johnsons, for example, say they encountered numerous frustrations, not only from prosecutors unable to successfuly make prosecutions under Virginia's complex building code, but also from judges willing to give builders the benefit of the doubt, and from skilled development lawyers capable of keeping builders immune from criminal penalties.

"We've done everything we could to try to get this house fixed up," said Nancy Johnson, 32, an English teacher at Northern Virginia Community College. But when they went to court, accusing their builder of building code violations, a judge turned on her husband, a Defense Department electronics engineer, she said.

Pointing a finger at her husband, the judge noted that Johnson had moved into the house without an occupany permit. "You're as guilty" as the builder, the judge snapped.

Ineffective building code prosecutions and the alleged bribery of inspectors are only part of the problem county officials say they face in controlling housing in a county that last year alone issued 1.812 residential building permits -- more than double the number issued in 1975.

The building boom has strapped the effectiveness of the county's 20-man inspection division, according to Charles J. Vincent, the director of the county's Department of Construction Services. With each home requiring as many as 15 separate inspections, Vincent said, each of his men sometimes must visit up to 40 sites a day.

"I can't guarantee the public every defect will be picked up" Vincent said, "Things will be missed."

Contractors are licensed by the state, but state officials can't assure home buyers that they can force compliance with building laws, Vincent said.

For example, Vincent said, contractors without state licenses can still legally build homes in some cases.

Under Virginia law, a builder is not required to have a license if he is the sole owner of his construction sites and if the homes he erected there aren't sold until the work is finished, according to A.C. Powers, assistant executive director of the state Registration Board for Contractors.

In the Montclair Country Club subdivision, built by Tray-Mare Construction Co. of Dumfries, a rash of home buyer complaints -- ranging from cracked foundations to inadequate insulation -- prompted the state to strip the Tray-Marc of its contractor's license. The state found the company guilty of "gross-negligence, continued incompetence and misconduct as a general contractor."

The company abandoned several unfinished homes in the Montclair subdivision, and its president, Stephen J. Siegel, moved to Florida.

But under loopholes in the state law, Siegel could resume building houses in Prince William, Vincent said, "If that guy came back to town tomorrow," Vincent said, "I can't deny him a (building) permit."

But builders here told investigators the inspectors must share the blame.

Chief Prosecutor Paul B. Ebert, who is overseeing the bribery investigation, said some builders claim inspectors have created an atmosphere that encourages payoffs.

"The major allegation the builders have is that (inspectors) are incompetent and unavailable," Ebert said, "and any gifts they may give are strictly to encourage competence and availability."

Ebert is no stranger to land development. At present, he said, he has an interest in two tracts under development in Prince William. He said he sees no conflict in serving both as a prosecutor and as a developer. His land development, he said, is restricted to subdividing lots and selling them to prospective home buyers or builders.

"I'm not a builder," he said. "There is no building inspecation involved" in his ventures.

Ebert noted that inspectors are not paid particularly well. Their annual salaries range from $11,000 to $19,000.

Investigators found that the gifts to inspectors included bottles of liquor, appliances and cash payments of between $20 and $100 at a time.

The former inspector implicated in the alleged scheme, Charles J. Wright, reportedly told prosecutors he was bribed more than eight times in the last two years.

No criminal charges have been filed against Wright, who recently resigned after serving for nearly six years. Sources familiar with the probe said Wright is cooperating with investigators, and he is expected to be a prosecution witness at the builders' trials.

Although only builders have been charges so far, county officials said investigators are looking into allegations involving Wright's fellow inspectors.

During construction, at least four different inspectors will visit a site They are grouped into four categories -- mechanical, plumbing, electrical and building -- based on their individual expertise. Wright, for example, was a building inspector. Each home he supervised was also checked by electrical, plumbing and mechanical inspectors.

When a house is completed and passes final inspection, the inspections division issues it an occupancy permit, certifying that it is safe to live in. Under state law no one is supposed to live in a house until it receives an occupancy permit.

But investigators found some cases in which builders moved home buyers into houses that did not have the permits.

In Tray-Marc's Montclair subdivision, investigators said, the company allowed homeowners to move into a half-dozen homes that had failed inspection and lacked occupancy permits.

When the Johnsons moved into their home at 4117 Mill Creek Rd. in the Mill Creek subdivision, their house had no occupancy permit, and neither did the homes of three of their neighbors.

The Johnsons said their builder, Jerry Lee Lewis, 34, of Haymarket, encouraged them to move in ahead of time and assured them that it was all right.

"There was no more than five days' work left on the house when we moved in," Johnson said, "but he never finished it."

The Johnsons and their neighbors turned to Vincent and the county inspections division for help. More than a dozen building code violations were subsequently found in their house.

When Vincent failed to get Lewis to correct the alleged defects, he brought criminal charges against the builder.

But the courts didn't help much.

Lewis was convicted in General District Court on charges of failing to obtain occupancy permits. But on appeal to Circuit Court, his lawyer, Claude Compton, a major Prince William development attorney, successfully argued that his client had not been properly notified of the alleged violations. State law requires the county to give a builder an opportunity to correct any defects before filling criminal charges.

Compton claimed the letter the inspections division sent Lewis was signed by an assistant to Vincent and should have been signed by Vincent himself.

Circuit Court Judge Percy Thornton Jr. agreed with the lawyer, and the charges were dismissed.

Vincent then brought new charges against Lewis, alleging several structural deficiencies in the Johnson home. But they, too, were dismissed on technical grounds.

Chief prosecutor Ebert, who did not personally try the Lewis cases, said the complicated building code is a vague, new law and judges seem inclined to give builders the benefit of the doubt.

Vincent has temporarily given up bringing criminal charges for building code violations.

And without the threat of successful prosecution, he said, he is almost powerless to enforce building regulations.

"It doesn't matter how much the public gets ripped off," he said, "It's a legal nightmare."

In court, he added, builders "are made out to be the victims, I'm made out to be the bad guy, and the homeowner is the one who suffers.