Four Northern Virginia residents and three area businesses pleaded guilty in federal court in Alexandria yesterday to conspiring over the past two years to use the United Parcel Service to sell thousands of items of drug paraphernalia in local shops.

Largely shutting down the sale of drug paraphernalia in Northern Virginia, the defendants also agreed to forfeit their inventories and stop the sale or manufacture of bongs (a type of pipe for smoking), scales and other products designed for illegal drug use.

"There's supposed to be a war on drugs in society, and this is part of that battle," said Assistant U.S. Attorney Lawrence J. Leiser, who prosecuted the case. "We do it now even to the level of attacking the instruments used to ingest illegal drugs."

The individuals and corporations who pleaded were the last remaining defendants in a case that surfaced in May when the U.S. Attorney's Office unsealed a 70-page, 302-count indictment against seven corporations and their executives. Other defendants had already pleaded guilty or have had charges against them dropped.

U.S. Attorney Henry E. Hudson said a ruling by U.S. District Judge T.S. Ellis III will make it easier to bring cases. Hudson said Ellis ruled that "the government does not have to prove that the merchant knew the purchaser wanted the product for the purpose of ingesting drugs."

The finding leaves it up to juries to determine whether a product is designed primarily for illegal drug use, prosecutors said. If a jury finds, for example, that a plastic pipe is made for smoking marijuana, then the retailer is guilty of selling drug paraphernalia, they said.

John K. Zwerling, attorney for Randall K. Dyer, of Springfield, said the ruling was a key reason his client and the others agreed to a government offer to drop dozens of charges if the defendants each pleaded guilty to one conspiracy count.

Those who pleaded yesterday were Dyer and his Alexandria-based Tobacco Accessories Distributing Co.; Page E. Wiencek and RPM Associates Inc., of Herndon; William L. Love, who owned an independent retail outlet in Manassas; and John Burgess, of Manassas-based Dragon Song Ltd.

Individuals agreed to forfeit 20 percent of their assets, and will be sentenced to no more than three years in prison and fined up to $250,000. Corporations face fines of up to $500,000. Ellis set sentencing for Nov. 9.