LOS ANGELES -- Despite objections from major league baseball, federal security officials decided Friday to allow banner-towing aircraft to fly over the two World Series ballparks.

The decision comes amid heightened concerns about terrorist attacks nationwide. FBI Director Robert Mueller told congressional panels Thursday that terrorists could strike again soon in the United States, while the CIA said the current situation is comparable to the summer before Sept. 11.

"What used to be seen as an absolutely fun thing like an all-California World Series from a security perspective, we look at through different eyes now,'' said George Vinson, special security adviser to Gov. Gray Davis. "That's been the case since Sept. 11. ... There is continual risk assessment.''

Friday's decision on flyovers by the federal Transportation Security Administration was a response to a major league baseball request to completely restrict airspace during games at Edison Field in Anaheim and Pacific Bell Park in San Francisco.

Baseball officials are concerned about "safety and security,'' said Kevin Hallinan, baseball's head of security. He planned to meet with lawyers to discuss the ruling.

Gordon Johndroe, spokesman for the national Office of Homeland Security, said there were no specific threats against the World Series.

Still, the California National Guard will deploy elite units at the ballparks to deal with possible threats involving biological, chemical or radiological weapons, said Capt. Denise Varner, a spokeswoman for the Guard.

The 22-member teams were previously used at the 2002 Winter Olympics in Salt Lake City and at last year's World Series in Arizona. They're equipped with devices that can analyze everything from air to infield dirt to detect anthrax and other hazardous materials.

On game days, the home ballpark will be closed and searched long before fans arrive. Neither stadium has metal detectors, but fans will be selectively screened for weapons and other contraband.

There could be four times as many police and security officers at Edison Field than during regular-season games, said John Drum, director of ballpark operations. They'll be stationed at key points, including dugouts, where they'll watch the stands between innings for disruptive fans.

At Pac Bell, the Coast Guard will be part of increased security in McCovey Cove, where boaters and swimmers troll for home run balls, said Jorge Costa, senior vice president of ballpark operations.

In addition, only 75 people at a time will be permitted to watch the game from a free, public viewing spot just outside right field. Every three innings, those fans will be asked to move on and another 75 will be allowed to watch.

Johndroe said timing kept the World Series from being designated as a national special security event, like the Super Bowl in New Orleans.

"The World Series is different from many events because there's relatively short notice about who the participants will be,'' he said.

Vinson said that has not hurt security because California has the resources to keep the games safe.

"These kinds of symbolic, densely populated events are a top priority for law enforcement,'' said terrorism expert Brian Levin, a former New York police officer who heads the Center for the Study of Hate and Extremism at California State University, San Bernardino.

The federal government has a standing airspace restriction over major sporting events prohibiting aircraft from flying below 3,000 feet and within three miles of the venue. The Transportation Security Administration, created after Sept. 11 as part of the federal airline security legislation, has at times granted waivers allowing aircraft to fly directly over stadiums after applicants undergo security checks.

An amendment to the Aviation Security Improvement Act proposed by Sen. John Breaux, D-La., would ban waivers for six months while the TSA takes public comment on a new rule. And in the House, Rep. Fred Upton, R-Mich., has been trying to attach a provision to the transportation spending bill that would prevent the FAA from issuing waivers.

TSA officials and some pilots suspect the pro teams' real concern is eliminating competition for advertising revenue.

As part of its decision Friday, the agency extended its restricted flight limit for the two stadiums to 5,000 feet and 5 miles, but it refused to revoke waivers already granted to commercial aircraft companies, said Niko Melendez, a spokesman for the agency.

The decision was made after weighing the current security-threat level against the right of access to airspace, he said. Citing security issues, he declined to say how many waivers had been granted.

TSA officials will be posted at airfields to make sure people who received the waivers are the ones who fly the planes, Melendez said.

Police had hoped the security agency would help them control airspace by completely restricting the aircraft.

"We do not want to impact commercialism, but we think security overrides that,'' said Anaheim police Sgt. Rick Martinez.