Four years ago sewer workers sank their drills at three locations in the Manassas area and installed pipes connecting sewer lines to storm water drains.

Although it was done by public employes, it was illegal, lacking permits required by the Virginia Department of Highways and Transportation and the State Water Control Board. The "midnight plumbing," as some officials call it, resulted in raw sewage being dumped by the Greater Manassas Sanitary District into the Occoquan Reservoir, the drinking water source for 600,000 Northern Virginians, officials said.

The secret piping, discovered only two months ago by a highway crew, led to only a mild reprimand for the sanitary district -- a letter telling it to plug the connections. The maximum possible penalty would have been a $10,000 civil fine and criminal prosecution.

"It's ridiculous," said Noman Cole of Fairfax County a former chairman of the control board. "We have such a double standard. If a private builder had done it that, the Board of Supervisors would have buried him."

One Virginia official said yesterday that for political reasons it is harder to pursue violations by public groups than private ones. Home builders agree. "If I had dug up a road without a permit, I would have fined right off the bat," said William Hazel, a Northern Virginia sewer line construction contractor.

Control Board officials say it is too expensive and time consuming to go after every violation through litigation. "Our main chore is to make sure that correction is done. Our board isn't after blood," said Thomas Schwarberg, who heads the Northern Virginia office of the Water Control Board.

The sewer district's purpose for installing the pipes four years ago was to prevent sewage from backing up into homes during heavy rains. These backups occurred because the sewage system was -- and is -- inadequate. The secret connections dumped the overflow the occurred during heavy rains into the storm sewers -- and eventually into the reservoir.

Christy Briggs, a pollution control specialist with the board, said that because the connections were under streets, there is no way of telling how -- much and when -- sewage flowed into the storm sewers.

John Sloper, administrator of the Greater Manassas Sanitary District attributed the failure to obtain the connection permits to administrative error and insisted there have been no overflows through the illegal connections in the past two years.

The Virginia Highway and Transportation Department concluded last month that sewage did enter the storm sewers during that period. "We felt that some sewage had run through at least two of the three bypasses" said D. E. Ogle, Manassas resident engineer with the department.

When the water board last month ordered the bypasses closed, Sloper requested a 120-day extension for one of the three connections.

Sloper said yesterday he asked for the extension, which was denied, so the system could retain the option to bypass in case of heavy rains. The threat of backups in private homes still exists, a problem Sloper said he believes -- as he did four years ago -- poses a greater danger in sanitation than does polluting the Occoquan.

Although the hidden connections violated the sanitary district's contact with the Upper Occoquan Sewage Authority, which requires all the district's sewage to be treated at its Centreville plant, the authority, also a public agency, has not acted against the sanitary district.

Millard Robbins, the authority's executive director, said it is hard for his group to punish the violators without knowing how much sewage was diverted from its plant.

Highway department officials have ordered the sanitary district to repair the damages done to storm sewers in installing bypasses and to pay for repairs to sidewalks that have settled because of the illegal connections.

Water Board officials said they will not pursue the case against the sanitary district unless they discover further violations.

Although the board received a letter from the sanitary district saying the illegal pipes had been closed, it has yet to inspect the locations -- two on Lafayette Avenue and one on Urbanna Road. "I'm taking their word for it," said the board's Briggs.