I know for a fact I was born with a gene for justice,” said Susan Gracey, a 72-year-old grandmother of two from Brookline, who dates her activism to a plea for better playing fields for the girls in her elementary school.

The Grannies unabashedly seek attention, and they usually succeed. Founded in 1987 in British Columbia by women whose targets ranged from nuclear submarines to clear-cut log ging, the Raging Grannies have expanded to a worldwide movement of more than 60 autonomous chapters, or “gaggles,” which include a Boston-area chapter with about 18 active members and a Western Massachusetts gaggle with 40.

Their activism has led to arrests — dozens of times for a few members — as the Grannies spread their message around the region at sites such as Army recruiting offices, high schools, and the gates of nuclear power plants. And while they use humor to attract attention, the members of this loosely organized group are deadly serious about their concerns.

In the South End on Sunday, amid the dreadlocks and scruffy beards of other protesters who dotted a rally against a nearby biological research lab, Gracey stood out with a broad-brimmed, hot-pink hat. With Jean Miller, a 69-year-old grandmother of eight from the Back Bay, Gracey held aloft the Raging Grannies banner and broke into song with the three other members.

In soft voices that competed with speeches lambasting the Boston University biolab, where scientists will study some of the world’s deadliest germs, Gracey and Miller offered these lyrics about Mayor Thomas M. Menino and the Bio safety Level-4 lab, which is under construction on Albany Street.

Set to the tune of “Frere Jacques,” the age-old children’s round, Gracey and Miller sang:

“Frere Menino, Frere Menino,

Dormez-vous? Dormez-vous?

Warning bells are ringing,

Raging Grannies singing,

NO L-4! NO L-4!”

The group isn’t limited to grandmothers and imposes no firm age threshold to join — members range in age from their mid-40s to 80s. But age, apparently, does play a role, along with zeal and talent.

“You don’t have to be a granny, only raging,” said Miller, a former teacher and nurse’s aide. However, she added, “you ‘d better not be gorgeous and 25, but you have to be able to sing.”

For the Boston gaggle, which began about 10 years ago, the songs are polished and rehearsed at twice-monthly meetings at Gracey’s home. One source of these songs is Maddy McDowell, 76, a grandmother of three from Cambridge whom Gracey called a “popcorn machine” of new compositions.

McDowell, a professional registered architect who recently joined the Grannies, relishes this outlet to combine creativity and public policy concerns. “This is a wonderful time of life because your obligations are done,” she said.

The protest Sunday was a typical setting for the Grannies, who walked to the South End biolab site from Roxbury, singing along the way and displaying their banner, which shows an outraged granny in full attack mode, an umbrella raised menacingly above her head. Other area demonstrations have included a rally at Faneuil Hall on April 28 to call for the impeachment of President Bush for, among other things, the Iraq war and the treatment of detainees at Guantanamo Bay.

“Fundamentally, I feel that if we don’t impeach Bush, we’re negating the Constitution and what it stands for,” said Gracey, a former teacher and court reporter who joined the Grannies about three years ago.

The Western Massachusetts chapter has been especially busy.

Last month, seven Grannies were arrested as they protested at the Vermont Yankee nuclear power plant in Vernon. On Wednesday, they sang against the expansion of a Wal-Mart in Hadley. And on Saturday, they marched in a gay pride parade in Northampton.

Despite their frequently controversial stands, the Grannies said, they never hear jeers. “I don’t think heckling Grandma is a cool thing to do,” Gracey said.

Not all the demonstrations end benignly. In November, five Grannies from Western Massachusetts were arrested in Greenfield when they refused to leave an Army recruiting office, where they had brought home-baked chocolate-chip cookies and an inexhaustible supply of rhetoric to try to persuade the recruiter to quit.

“We sang some anti recruiting songs,” said Paki Wieland, 63, of Northampton, who also was arrested at Vermont Yankee. “At some point, [the recruiter] said, ‘This has been all well and good, but I have some work to do.’ ”

The Grannies, though unfailingly civil, remained undeterred. They told the recruiter: “This is where the rub comes, because we have work to do, too, and our work is to make sure that you stop your work,” Wieland said.

The state eventually reduced the charges from criminal trespassing to civil infractions. The women were “found responsible” for trespassing, but last month District Judge Herbert Hodos declined to fine them $50 each, as prosecutors had asked.

Among the Boston gaggle, neither Gracey nor McDowell has been arrested, and Miller said she can’t afford to be incarcerated because she helps care for her grandchildren.

But that doesn’t mean their zeal for nonviolent protest is diminished.

One example of that fiery emotion is part of an antiwar song that Gracey wrote to the tune of the World War I anthem “Over There”:

“So beware! Just take care!

Listen up! Read our lips! ‘Cuz we swear

That we are Grannies, and we are Raging,

And we WON’T SHUT UP

‘Til it’s over over there!”