The federal government is opening close-in parking lots at the country's biggest airports that have been off-limits since Sept. 11 because of worries about car bombs.

Federal officials also will change the way air travelers are screened after they pass through security checkpoints over the next few weeks, checking them only at randomly selected gates, said Robert Johnson, spokesman for the Transportation Security Administration.

"We're trying to avoid screening grandma two or three times as she makes her way home for the holidays," he said.

Johnson said the prohibition on unattended vehicles parking within 300 feet of a terminal was being dropped Monday as long as the terrorist threat level is at code yellow, or "elevated," the middle of a five-point scale of risk developed after the terror attacks.

TSA chief James Loy was announcing the change at a conference co-sponsored by the Airports Council International-North America and the American Association of Airport Executives.

The 300-foot rule will be reimposed if the threat level rises to orange or red, Johnson said.

Airports, though, must draw up plans outlining how they would deal with the threat of an explosion. They won't have to close the parking areas during an elevated threat if their plans don't call for that, Johnson said.

New layers of airport security allow the rules to be eased, Johnson said. He cited a better-trained screener work force, federal air marshals, background checks of people who work beyond airport security checkpoints and screening of checked baggage at 252 airports.

Todd Hauptli, a spokesman for airport operators, said the facilities have pushed the TSA hard to let them reopen their close-in parking lots.

"This has been a thorn in the side of many airports," and the rule brought no significant improvement security, he said.

Not only do some airports lose money because they've closed parking, they have to bus people from remote parking lots, Hauptli said. "It's definitely a passenger convenience, customer convenience issue."

Like the parking restrictions, screening passengers just before they board their plane was on a "stupid rule" list that Loy drew up. He promised to look at the list and try more commonsense approaches.

As part of that effort, the TSA will change boarding-pass procedures at all or part of eight airports, adding to the nine that are in a pilot program to eliminate gate screening.

Requiring boarding passes before passengers pass through security allows airports to conduct thorough screenings for selected passengers at the security checkpoints rather than the gates.

Johnson said there's only a very slim chance these passengers would be screened again when they arrive at the gates.

He said the boarding pass procedures will be changed at Milwaukee's Gen. Mitchell International Airport, Cincinnati/Northern Kentucky International Airport, Houston's Bush Intercontinental Airport, Boston's Logan International Airport, Memphis International Airport, Charlotte/Douglas International Airport in North Carolina, Seattle-Tacoma International Airport and Pittsburgh International Airport.

The nine airports already in the pilot project are Los Angeles; Long Beach, Calif.; Newark, N.J.; Detroit; Minneapolis/St. Paul; Miami; St. Louis; and LaGuardia and Kennedy in New York.

At all other U.S. airports, mobile teams of screeners will check passengers a second time at randomly selected gates, Johnson said.

"It will be random and unpredictable to the public," he said, and the numbers who get screened "will go up and down."

Hauptli said the practical outcome of the new policy is that fewer people will get screened a second time.

David Stempler, president of the Air Travelers Association, said the gate screening was one of the most hated new security hassles at airports.

"Clearly, the gate screening resulted from the inadequacies of their [federal officials'] original security program," he said. "Now that they have started to correct those deficiencies, they can eliminate the much-despised gate screening."