WASHINGTON -- Moving swiftly to enforce a new federal criminal law against abortion clinic blockades, the Justice Department charged six people yesterday with trying to shut down a clinic in Milwaukee over the weekend.

The 12-day-old law makes it a crime to use force, the threat of force or "physical obstruction" to try to stop abortions.

The law's constitutionality is under challenge in five federal courts across the country, but no judge has granted opponents' pleas to stop the federal government from enforcing the law. The first judicial ruling on that request is expected Friday in a federal court in Alexandria, Va.

In the first criminal case pursued under the law, the U.S. attorney in Milwaukee charged that five men and a woman blocked the two entrances to a clinic in the Wisconsin city on Saturday by linking themselves and a car and a station wagon together with handcuffs, chains, steel bars, pipes and a 55-gallon drum filled with concrete.

As a result, an FBI agent said in a sworn statement, the clinic opened three hours later than planned. It was scheduled to handle 37 patients for abortions and other "reproductive services" that day, but only 20 actually were treated there, the statement said.

Deval L. Patrick, the assistant attorney general in charge of civil rights, said in announcing the charges: "Congress carefully drew a line between lawful protest and the rights of others. When that line is crossed, we will enforce the law as Congress wrote it."

Last night, U.S. Magistrate Judge Patricia Gorence released four of the six on personal recognizance bonds.

Abortion opponents, in their federal court challenges, contend that the law goes beyond force, violence and obstruction, and makes it a crime to engage in several forms of peaceful protest.

Abortion rights groups counter that the law was written in a narrow way to make sure that it outlawed only blockades or violence at clinics, or other forceful attempts to shut them down.

In the Milwaukee case, the FBI agent's statement said, those involved had cut holes in the car's exterior panels and inserted their hands or legs through those holes, then linked them by handcuffs, chains, reinforcing rods or pipes -- some welded to the cars' metal surfaces.