''We're here tonight to send a message to John Kerry: Oppose the dangerous, reckless, and unnecessary war,'' yelled Eric Weltman, organizing director of Citizens for Participation in Political Action, as he addressed the crowd by bullhorn in the parking lot of the John F. Kennedy Library.

The group had planned to stand at the entrance to the library, where Kerry, who is campaigning for the Democratic presidential nomination, was delivering an environmental speech, but Boston police officers pushed them more than 100 yards away, citing the nation's heightened state of alert for a terrorist attack.

Some protestors held signs reading, ''John Kerry, War Monger: Kiss Your Votes Goodbye'' and ''Dorchester wants peace.''

While Kerry aides said the senator was not troubled by the protest, one of the first that has greeted him on the presidential campaign trail, he came to the library by a driveway that was closed to all other traffic and entered the building by an entrance behind and beneath the building.

Speaking with reporters before his speech, Kerry expressed respect for the protesters and their willingness to gather on a night when the temperature hovered in the teens. Nonetheless, the senator stood by his vote last fall in favor of a congressional resolution authorizing military force to disarm Iraq of any weapons of mass destruction.

''I understand it; I've been there,'' said Kerry, who came back from serving in the Vietnam War to join the antiwar movement. ''But I also believe that we're living in a different moment in history with a different kind of threat, and that is proliferation, the greatest threat that the world faces.''

Also, Kerry said that while President Bush declared last week that it is ''game over'' in terms of dealing with Iraq, he believes there is still at least another month before the US forces will be able to launch an attack.

''It seems to me there's a time to rattle the saber louder and raise the rhetoric while you're doing good diplomacy,'' Kerry said. ''I understand the need also to be very tough and clear about your intentions, in order to make it clear to Saddam Hussein that this is for real, and there's a balance. But I'm reminded when I came back from the Vietnam War, I remember reading Edmund Burke, who said that a `conscientious man would be cautious how he dealt in blood.' And it strikes me that the United States of America has the solemn obligation to show its conscience in its approach to this kind of an issue.''