Filed at 8:07 p.m. ET

AUGUSTA, Maine (AP) -- In a banner day for advocates of gay marriage in New England, Maine's governor signed a freshly passed bill Wednesday allowing the practice and was followed closely by the endorsement of the New Hampshire Legislature.

If New Hampshire Gov. John Lynch signs the bill or lets it become law without his signature, his state would become the sixth overall to allow gay marriage and the fifth in New England. Rhode Island would be the region's only holdout.

Maine Gov. John Baldacci, a Democrat who hadn't indicated how he would handle his state's bill, signed it shortly after the legislation passed the Senate on a vote of 21-13 -- a margin not large enough to override a veto.

''In the past, I opposed gay marriage while supporting the idea of civil unions,'' Baldacci said in a statement read in his office. ''I have come to believe that this is a question of fairness and of equal protection under the law, and that a civil union is not equal to civil marriage.''

The bill authorizes marriage between any two people rather than between one man and one woman, as state law currently allows. The House had passed the bill Tuesday.

The law is to take effect in mid-September but could be sidetracked before then. Opponents promise to challenge it through a public veto process that could suspend it while a statewide vote takes shape.

Sue Estler, of Orono, said she and her partner of 20 years, Paula Johnson, plan to get married. But she also thinks opponents might collect enough signatures to force the referendum.

A professor at the University of Maine, the 64-year-old Estler said she sent an e-mail to out-of-state friends and family members Wednesday saying ''Oh, my god. The governor just signed the bill.''

''But I said, 'Don't make your travel plans for the wedding yet. There's still probably a referendum to go,''' she said.

Legislative debate in Maine was brief. Senate President Elizabeth Mitchell, D-Vassalboro, turned the gavel over to an openly gay member, Sen. Lawrence Bliss, D-South Portland, to preside over the final vote.

Republican Sen. Debra Plowman of Hampden argued that the bill was being passed ''at the expense of the people of faith.''

''You are making a decision that is not well-founded,'' warned Plowman.

Both states' bills specify that religious institutions are not compelled to recognize same-sex marriages.

The activist group Gay & Lesbian Advocates & Defenders has targeted all six New England states for passage of a gay marriage law by 2012.

Connecticut has enacted a bill after being ordered to allow gay marriages by the courts, and Vermont has passed a bill over the governor's veto.

Massachusetts' high court has ordered the state to recognize gay marriages. In Rhode Island, a bill to legalize same-sex marriage has been introduced but is not expected to pass this year.

New England states have acted quickly since gay marriages became law in Massachusetts in 2004 because it's a small region with porous borders, shared media markets and a largely shared culture, said Carisa Cunningham of the gay defenders group.

Outside New England, Iowa is recognizing gay marriages on court orders. The practice was briefly legal in California before voters banned it.

If it comes to a statewide vote in Maine, Estler is confident gay marriage will prevail.

''I think Maine people will support it,'' she said. ''Part of the reason I say that is Maine is a state where people, regardless of party affiliation, really believe in live and let live.''

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Holly Ramer reported from Concord, N.H. Associated Press writer Clarke Canfield in Portland, Maine, contributed to this report.