BOSTON -- Lawmakers voted Thursday to keep a constitutional amendment that bans gay marriage off the 2008 ballot during a joint session of the Massachusetts House and Senate.

The 151-to-45 vote blocked the amendment that defined marriage as a union between one man and one woman from going before voters next year.

"Today's vote was not just a victory for marriage equality. It was a victory for equality itself," Gov. Deval Patrick said.

The amendment needed the support of 50 of the state's 200 lawmakers in two consecutive sessions. The amendment passed with 62 votes on the final day of the last legislative session earlier this year, but it only received 45 votes on Thursday.

"We're proud of our state today, and we applaud the Legislature for showing that Massachusetts is strongly behind fairness," said Lee Swislow, executive director of Gay & Lesbian Advocates & Defenders. "Equality for gay and lesbian citizens has enriched our state, made our communities stronger, and our families happier. The vote today was the triumph of time, experience and understanding over fear and prejudice."

The Legislature has twice put off voting on the controversial issue by adjourning without taking a vote after state residents collected petitions asking that the question be put to the voters as a ballot question. The supporters of the gay marriage ban amendment collected signatures from 170,000 people in an effort to get the question on the 2008 ballot.

"My spouse, my two children and the thousands of other couples and their children, who've married in the last three years can finally sleep easy tonight knowing that my rights and my children's are going to be protected," Sen. Jarrett Barrios said.

The Massachusetts Family Institute expressed outrage, citing pressure by Gov. Deval Patrick, House Speaker Sal DiMasi and Senate President Therese Murray for urging lawmakers to switch their position during the 11th hour.

"The Marriage Amendment won its first legislative vote and was on track to win its second with a healthy margin. The unprecedented pressure by leaders on Beacon Hill -- the rumors of patronage jobs by Gov. Patrick and arm-twisting by House Speaker DiMasi -- derailed the largest initiative petition drive by citizens in the commonwealth's history, and this is a brutal loss for citizen-centered democracy," Massachusetts Family Institute President Kris Mineau said in a statement.

More than 8,500 same-sex couples have married in Massachusetts since they became legal in May 2004. The Bay State remains the only state in the nation to allow same-sex couples to marry.

Earlier in the day, activists on both sides of the issue gathered at the Statehouse to make their voices heard. Preaching a message of marriage equality, members of the Religious Coalition for the Freedom to Marry marched from St. Paul's Cathedral to the steps of the statehouse.

"God loves all of God's children -- gays, straight, transgender and bisexual -- and everyone has equal rights," the Rev. Anne Rousseau said.

Opponents of gay marriage demanded that the issue be decided by the voters of Massachusetts.

"If the majority of people in Massachusetts think that marriage should remain between a man and a woman, they ought to say that," said Wally Atwood, who supports a gay marriage ban.

"To take the position that a small group of unelected judges can determine who we are as a people, I think it's not right," said Elizabeth Dionne, who supports a gay marriage ban.

"This is a clear issue of civil rights and social justice, and we are here in support of it," said Alex Coleman, who supports gay marriage.

The issue has made national headlines with Democratic lawmakers. U.S. House Speaker Nancy Pelosi lobbied to keep the question off the ballot.

"I think it's a choice people of Massachusetts need to make. Not Nancy Pelosi. She is not from here. She has nothing to do with it," Dionne said.

Others, such as Joan Fahey, who married her long-time partner in 2004, said that the issue transcends politics.

"It will really impact (us) on a day-to-day basis to the extent that gays and lesbians feel safe in this state," she said.