Just before the Republican National Convention, thousands of abortion rights activists marched over the Brooklyn Bridge into downtown Manhattan to decry what they termed a genuine terrorist threat -- efforts by the Bush administration to curb women's reproductive rights.

The march comes amid a flurry of protests and rallies, symbolic and otherwise, as the Republicans prepare to open their convention Monday in this overwhelmingly Democratic city. In Central Park, Quakers and the families of soldiers killed in the Iraq war laid out 972 pairs of combat boots to symbolize those who have lost their lives. On the Long Island beaches, antiwar activists flew an airplane trailed by a large banner reading "Give Bush a Pink Slip."

And at Ground Zero, another group opposed to the policies of President Bush sounded 2,749 bells -- one for each victim of the Sept. 11, 2001, attacks.

FBI agents and New York City police, meanwhile, arrested two men on charges of conspiracy to plant bombs in a Midtown Manhattan subway station. Police Commissioner Raymond W. Kelly noted that neither man is believed to have connections to terrorist organizations, and that they had not obtained explosives.

The men allegedly drew a rough sketch of the Herald Square subway station at 34th Street in Manhattan, and scouted other potential targets from the Verrazano Narrows Bridge to a prison and three police stations, Kelly said. One of the men, Shahawar Matin Siraj, 21, lives in Queens and is a Pakistani national. The other man, Shames El Shafay, lives on Staten Island and is a U.S. citizen. They are being held without bail.

"It's important to stress that to the best of our knowledge they had no connection to international terrorism," Kelly said at a news conference. "But it's clear they had an intention to cause damage and kill people."

On the protest front, large swarms of bicyclists had slowed and in some cases blocked traffic Friday evening in the East Village and near Madison Square Garden, the convention site. Police arrested 264 bikers. As of Saturday evening, 20 to 40 of these protesters were still being held, legal advisers for the activists said.

There was little trouble elsewhere, however. At the Brooklyn Bridge on Saturday, marchers waving placards and pushing baby strollers -- and the drag-queen Church Ladies for Choice -- streamed across for more than hour before they poured into City Hall Park in Lower Manhattan. One 9-year-old held a sign saying, "More trees, less Bushes."

This march had an air of celebration, as a federal court judge struck down as unconstitutional last week the administration's ban on late-term abortions, because the law did not contain an exception for the pregnant woman's health.

"This decision was a reminder to people that this is the first administration to sign a law banning abortion," said Joan Malin, executive director of Planned Parenthood of New York City, which organized the demonstration.

For many veterans of the abortion rights movement, the march was part of a four decade-long struggle for health rights and access to abortion services. But many of the younger women spoke in the vocabulary of this age of terrorism.

"The administration is cutting health care for women and the right to choose," said Radikelly Kupowski, 24, one of the Radical Cheerleaders. "That's terrorism for women."

Amid the crowd, Charles "Chick" Straut appeared to have lost his way. In his baby blue button-up shirt and reversed cleric's collar, Straut read the newspaper quietly on a park bench as he waited to cross the East River. A retired Methodist pastor, he is a three-decade veteran of the abortion rights movement. "I grew up in a Republican atmosphere, and I took it for granted that abortion was an awful, sinful thing," he said. "But when I began to meditate on it, it wasn't so simple."

Security was heavy at this parade, as it was across the city on this hazy summer day. Police officers on foot and motorcycles followed the marchers, while police helicopters circled overhead. But the mood was as often buoyant, perhaps captured best by Brooklyn Borough President Marty Markowitz (D), an effervescent man. He stood on the bridge and cheered the marchers as they walked to Manhattan.

"You're leaving the city of Brooklyn," he yelled. "Have a good rally and come home soon."

Nita Praditpan, left, and Laura Moore, both of Manhattan, were among thousands of abortion rights activists protesting President Bush's policies in an event marked by high security and high spirits.