WASHINGTON (AP) _ Prosecutors do not need to prove that defendants charged with selling drug paraphernalia knew the buyer would use the items with illegal drugs, the Supreme Court ruled today.

The court's unanimous decision in an Iowa case said prosecutors need only show that a defendant knew customers are likely to use the items in connection with drugs.

''Requiring that a seller of drug paraphernalia act with the 'purpose' that the items be used with illegal drugs would be inappropriate,'' Justice Harry A. Blackmun wrote for the court.

''It is sufficient that the defendant be aware that customers in general are likely to use the merchandise with drugs,'' Blackmun said. ''Therefore, the government must establish that the defendant knew that the items at issue are likely to be used with illegal drugs.''

Today's ruling upheld a Des Moines woman's conviction on drug paraphernalia charges.

During a search of Lana Christine Acty's home and business, Posters 'N' Things, officials confiscated pipes, scales and chemicals often used to dilute illegal drugs.

Acty and the business were convicted in 1990 of conspiracy and using interstate means in a scheme to sell drug paraphernalia. She also was convicted of aiding the manufacture and sale of cocaine, money laundering and other related charges.

Acty was sentenced to nine years in prison and fined $150,000, and her company was fined $75,000.

Federal law specifies that some items, such as water pipes, are drug paraphernalia. The trial judge gave jurors a list of rules to use in deciding whether other items qualified as drug paraphernalia.

The judge told jurors they must decide whether Acty knew ''the nature and character of the items,'' but did not require them to decide whether she intended that they be used with illegal drugs.

The 8th U.S. Circuit Court of Appeals agreed with that interpretation of the law in July 1992.

Acty's lawyers had told the Supreme Court that none of the items seized in the search was primarily intended for use with drugs. Prosecutors should have been required to prove that she intended such use, they said.

But Justice Department lawyers said the law only requires proof that a defendant knew the items are used primarily with illegal drugs.

In today's ruling, Blackmun said, ''Although the government must establish that the defendant knew that the items at issue are likely to be used with illegal drugs, it need not prove specific knowledge that the items are 'drug paraphernalia' within the meaning of the statute.''

The case is Posters 'N' Things vs. U.S., 92-903.