The U.S. Customs Service, faced with allegations that it conducts abusive searches of airline passengers in its efforts to ferret out drug smugglers, announced yesterday that it will seek the approval of a federal magistrate when detaining travelers for more than four hours.

Customs Commissioner Raymond W. Kelly said the policy change would take effect Oct. 1. At most airports and other border crossings, Customs can detain passengers for lengthy periods--sometimes days--without court approval. The procedure has helped engulf Customs in allegations that it wrongly targets blacks and Hispanics as suspected smugglers.

During the detentions, Customs officers use "personal searches," such as pat-downs and strip searches, to help catch smugglers who hide cocaine or heroin in their clothes or swallow packets of the drugs. But the searches no longer seem as effective as in past years, officials said. Fiscal 1998 data, for example, show that of the 3,017 passengers who had to take off part of their clothing for a Customs inspection, only 28 percent were carrying illegal drugs.

Yesterday, in a meeting with reporters, Kelly said his decision to bring federal magistrates into agency operations would help ensure that Customs inspectors have a "reasonable suspicion" to continue detaining travelers.

"We're taking people's liberty away. We want judicial review of that. We want oversight as soon as reasonably possible," Kelly said. If the judge decides there are no reasonable grounds to continue holding an airline passenger, Kelly added, then the traveler will be released.

If reasonable suspicion is present, Customs may continue to hold the person and may ask for consent to medically supervised body searches. If consent is not given, Customs would have the option to proceed with X-rays, physical exams and the monitoring of bowel movements.

Customs's broad power to detain and search passengers has been upheld by the Supreme Court, but the tactics used have drawn strong criticism and lawsuits in recent months.

In May, a House Ways and Means oversight subcommittee, at the request of Rep. John Lewis (D-Ga.), held a hearing on Customs searches and whether they involved "racial profiling."

At the hearing, a Hispanic woman from New York said she was detained in 1994 for 25 hours at San Francisco International Airport, strip-searched, forced to take laxatives by Customs agents and not allowed to make phone calls. A black Florida woman testified that she was detained for two days in Miami in 1997, handcuffed to a hospital bed rail and forced to take laxatives, even though she was seven months pregnant at the time. Neither was carrying drugs.

Kelly, who took over at Customs a year ago, has moved swiftly to address such criticism by revamping the lines of authority, transferring senior officials and cracking down on misconduct.

Under Kelly's new rules, supervisors must approve pat-down searches. If agents want to take travelers off airport grounds to hospitals for intrusive body searches, they must receive approval from the top Customs official at the airport, in consultation with government lawyers.

Kelly also named an outside commission to investigate allegations of racial bias in the agency. The panel should submit its recommendations by early next month, Kelly said.

Customs installed a new computerized system in May to collect data on the race, sex, age and citizenship of airline passengers who undergo searches. Previously, the agency did not gather demographic data on a consistent basis.

Using race as a criterion to search travelers "is certainly not part of our policy. We have strongly prohibited that in our [employee] handbook, but we want to make certain it is not part of our practices," Kelly said.

Lewis called Kelly's decision to involve a federal magistrate in detention cases "a necessary step and a right step."

In another policy change, Kelly said Customs would try to help airline passengers resume their trips when detained but found not to be smuggling drugs. For passengers with interrupted travel plans, Kelly said Customs would help arrange for a new flight or an overnight hotel stay and pay for those expenses.

CAPTION: Customs chief Raymond W. Kelly has named an outside commission to investigate allegations of racial bias in the agency. He expects recommendations by early next month.