Local homeless advocacy groups will participate this summer in the first nationwide effort to register homeless people to vote, homeless activists said yesterday.

The campaign, which is being led by the National Coalition for the Homeless, hopes to inform this largely ignored population of its voting rights, Leah D. Mahan of the Massachusetts Coalition for the Homeless said yesterday.

"The estimate is that there are up to three million homeless people in the U.S.," Mahan said. "A lot of [them] don't know they can vote."

Under Massachusetts law, anyone with an address can vote, Mahan said. Since homeless people are permitted to use the address of a shelter or a former residence, they can legally cast ballots in November.

The homeless are a particularly difficult group to involve in politics, according to Dick Doyle, co-director of the Homeless Civil Rights Project, a group which will work with the coalition on the campaign.

"Homeless people are pretty tough to get a hold of," he said. "They can't afford newspapers, they don't see TV. You have to go to where they are."

Stanley L. Donald, the sales coordinator for Spare Change, a newspaper published by Boston-area homeless people, will be helping with the campaign in Cambridge. Donald said he hopes that weekly movies, as well as coffee and doughnuts, will attract people to a voter registration table he plans to set up on MIT property.

Activists will visit homeless shelters and soup kitchens in order to apprise the homeless of their right to vote, Doyle said. But they will also seek out homeless in Boston Common, in churches, and on the streets.

"It's a bombardment. We have posters, filers, we go down at mealtimes," Doyle said. "It means standing on top of a soapbox every chance you get."

Doyle said that homeless people are especially vulnerable to the political apathy that affects the public.

"The average homeless person is at the bottom rung of existence," Doyle said. "He says 'What the hell have I got to vote for?' You've got to turn him around."

Mahan said that her group will not advocate any political candidates in November.

"We make sure they know where the candidates stand," she said. "We try to lay it out there for people to make their own decisions."