First, air travelers had to submit to an electronic wand waved over the body. Then they were asked to remove their shoes. After that, their checked luggage was opened and searched. Now, with the nation under a Code Orange alert, local police are pulling over drivers as they approach airport terminals for random searches of their vehicles.

The searches at all three major Washington area airports and across the nation have met resistance in some cities as airport managers assess their legality. The measures, ordered by the federal agency in charge of airport security, have been criticized by civil liberties groups and prompted legal scholars to question whether random searches imposed by the federal government violated states' rights.

At least one major airport, Seattle-Tacoma International Airport, said it would not comply with the directive because it ran counter to state laws prohibiting police from searching a vehicle without a specific reason. "We can't just stop everybody, or stop every third car or every blue car," said airport spokesman Bob Parker.

The Transportation Security Administration instructed local police on Feb. 8 to begin the searches "in response to threats and intelligence information" it received. In the past, the agency has required some airports to search vehicles at parking lots or garages near terminals, but it has never before ordered random checks at arrival and departure curbs.

Some airport managers balked at following the directive until the TSA clarified the legal issues. In its defense, the agency pointed to several cases in which federal courts ruled that vehicles could be searched for reasons of public safety.

"We have legal standing to do this and do it in a constitutional manner," said TSA spokesman Robert Johnson. "Where there is a conflict, we'll work through that with local jurisdictions."

Now police at most airports, including the Washington region's three airports, are randomly inspecting cars and trucks that drop off or pick up passengers. They also are searching delivery trucks and other vehicles entering the airport.

Police at Harrisburg International Airport in Pennsylvania have been sweetening the inspections by passing out lollipops to targeted drivers. "It's so we don't intimidate," said Alfred Testa Jr., the airport's aviation director. "The policemen are very polite. They will have a smile on their face."

At some airports, such as Los Angeles International and Dallas-Fort Worth International, police have set up a presence similar to a sobriety checkpoint or a border crossing, where tens of thousands of drivers are told to slow down and officers visually inspect cars, waving some through and motioning others to pull over for a search.

Constitutional experts said the TSA could face a fight over the new rules. "There is a serious constitutional question about whether the federal government can direct local law enforcement agencies to do anything," said Georgetown University law professor Mark Tushnet.

The American Civil Liberties Union said airport officials in Pittsburgh, Philadelphia and San Francisco contacted their local ACLU chapters with questions about the policy.

Minneapolis-St. Paul International Airport stopped the inspections for several days last week, then resumed them after posting signs warning drivers that they might be searched. Most airports have posted similar signs. "There were enough questions that we decided to suspend the program," said airport spokesman Paul Hudson. Now, "We're happy with it."

The ACLU asked to meet with federal security officials to discuss the directive but has not received a response. "Like many airport authorities, we are struggling to understand what TSA has in mind, how it will operate and whether it will work," said Barry Steinhardt, director of the ACLU's Technology and Liberty Project. "We have lots of questions about whether these measures are going to be effective. . . . Flailing around is not good security."

How airports conduct the searches may have a strong bearing on whether they are ultimately deemed legal -- a question that remained unanswered yesterday, said airport executives and lawyers familiar with the issue.

Legal scholars likened the TSA directive to instances in which police have erected roadblocks to combat drunk driving or the smuggling of illegal aliens. Such steps typically are legal, so long as they are designed to promote public safety rather than to nab a specific criminal, Tushnet said.

In similar cases dating back to the 1970s, the Supreme Court has encouraged government officials to give people an alternative to vehicle checkpoints and urged police officers to perform searches that are not overly invasive, legal experts said. To comply, most airports have set up the inspection sites far enough away from the terminal so that drivers could decide to turn around and leave before entering the terminal area.

Important legal considerations include whether every driver will be stopped at a checkpoint or whether some will be selected at random, which potentially raises concerns about security officers improperly targeting drivers based on their race or religion, said Steinhardt.

Another open issue is whether drivers will be ordered to get out of their vehicles or will merely be asked a few simple questions about the cargo they are carrying. If police find evidence of a crime in the course of their search, it is generally admissible in court.

"The searches have to be standardized and minimally intrusive," said Washington law professor David Cole. "On the other hand, there's a very strong safety interest at play. People who want to wreak havoc with the airlines could attack outside rather than on the plane."