MANILA, Philippines -- Thousands of university students and other activists marched Saturday to protest President Bush's visit to this city already tense over security concerns.

Up to 4,000 protesters burned U.S. flags and an effigy of a pirate-dressed Bush as his motorcade sped by on the opposite side of the highway en route to the House of Representatives, where he addressed a joint session of Congress.

Waving anti-U.S. placards and streamers saying "Ban Bush" and "Bush No. 1 terrorist," the protesters were cordoned off by anti-riot police and Philippine marines.

Security forces effectively blocked Bush's view of the demonstrators by lining up tall army trucks along the middle of the road. Some protesters stood on top of the vehicles to raise their streamers.

The crowd chanted: "Bush, Bush, go away, take with you GMA," a reference to Philippine President Gloria Macapagal Arroyo.

The president's speech to Congress was nearly an hour late because of concerns about large crowds -- both supporters and protesters -- on his motorcade route. U.S. officials privately said demonstrators on or near the route posed the biggest problem.

Seven legislators walked out of Bush's speech, but plans for a larger walkout fizzled. One briefly flashed a banner -- which looked more like an oversized handkerchief -- that read "Mr. Bush, stop your war." The lawmaker was immediately warned by congressional staff to put it away.

Rep. Liza Maza from the leftist political party Bayan-Muna donned a shawl showing a Filipino bird, a broken missile and "No to U.S. war."

The protesters were calling for an end to U.S. military aid to the Philippines -- which they alleged was being used to suppress human rights -- the pullout of U.S. troops from Iraq, and an end to joint military exercises between U.S. and Philippine troops.

"We do not need their guns, helicopters and bombs," said Teodoro Casino, secretary general of the leftist group Bayan. He said the weapons and military hardware "will be used to wage war on our fellow Filipinos."

Leaders said similar rallies were held in at least nine other cities in the country.

Thousands of riot and traffic police were deployed on major thoroughfares in Manila to keep protesters away. Many downtown roads were blocked or traffic rerouted for Bush's motorcade, causing traffic jams.

At Ninoy Aquino International Airport, authorities halted or delayed some flights as part of stringent security measures.

Security was also tight at Manila train stations, where black-clad anti-terror police squads with bomb-sniffing dogs kept watch. In December 2000, 22 people were killed in a series of bomb attacks at one station and other places by suspected Muslim militants.