Last summer, when a Prince William County ranger called in county police to enforce a longstanding ban against drinking beer in public at county parks, park officials made an embarrassing discovery:

The police could not do it because the newly revised county code book no longer contained the former prohibition.

"Needless to say, we were quite surprised," Rich H. Artenian of the county park authority said last week. "We checked into it and found something of a mistake, an oversight, in the county code that had just been rewritten."

The mistake was corrected last week when the county Board of Supervisors voted unanimously to revise the code and ban alcohol in public parks except in cases in which the state issues a special permit. The revision was passed without comment after a public hearing at which no one spoke.

Artenian said that the county, like most counties in Northern Virginia, bans alcohol in public parks because of a state law that makes drinking in public illegal.

"Really, the only place you can drink in Virginia is on your own property or in an establishment with a liquor license," Artenian said. "Even without a specific county code, drinking in parks is illegal anyway. The people caught drinking last summer could have been stopped under state law."

Groups or individuals may apply for a state permit allowing alcohol at special functions, he said. The permits cost $35 and take 10 days to process.

Artenian said that an area where alcohol is being consumed must be roped off from the general public, and county park rangers will check periodically to see if all is going well. He said that the county processes from 50 to 70 alcohol permits each summer.

Those caught drinking alcohol without a permit are asked to leave the park or throw away whatever they are drinking, he said, adding: "Our rangers are there for informational purposes, not to bust people."

Park Authority Controller Peggy Delinocci said that most of the county's residents approve of the ban on drinking.

"Drinking creates an atmosphere that may not be conducive to having young people about, and parks are primarily used by families with children," she said.