UPDATE 1-New Hampshire lawmakers reject gay-marriage bill

* House blocks bill by slim two-vote margin

* Exemption for religious institutions sticking point

* Bill faces further debate and possible governor veto (Adds details, reaction)

By Andrew J. Manuse

MANCHESTER, N.H., May 20 (Reuters) - New Hampshire lawmakers unexpectedly rejected a bill on Wednesday that would have made the state the sixth in the United States to authorize gay marriage.

The state's Democrat-controlled House of Representatives voted down the bill in a 188-186 vote, hours after its Senate approved the legislation 14-10 along party lines. An earlier version of the bill passed the lower chamber on March 26.

The legislature had been asked to approve language that would give legal protections, including the right to decline to marry same-sex couples, to clergy and others affiliated with religious organizations.

That wording was added by Governor John Lynch, a Democrat who promised to sign the bill if those changes were made.

The House vote against the governor's amendment means the bill will be sent to a committee that will try to resolve the differences between the two chambers. It remains unclear how the governor would respond to any changes to his wording.

Lynch has said he would veto gay marriage if his wording is not adopted.

State Representative Steve Vaillancourt, a gay Republican from Manchester, was a leading voice against the amendment securing religious liberties, saying that the House should not be "bullied" by the governor.

Vaillancourt said an earlier bill that did not provide protections to clerics or religious groups was the one that should have been passed, adding that the amended bill would allow discrimination to be written into state law.

The earlier bill passed both chambers.

Other House Republicans said they voted against the current bill because the process did not fairly give a voice to every citizen who wanted to speak on the issue.

The debate comes five years after the nation's first same-sex marriages took place in neighboring Massachusetts.

Connecticut last year became the second state to legalize gay marriage. In April, Iowa and Vermont followed suit. This month, Maine's governor signed a gay-marriage bill and the New York State Assembly passed similar legislation.

If the bill had passed in New Hampshire, five out of six New England states would have authorized legislation authorizing gay marriage, making tiny Rhode Island, with its large Roman Catholic population, the region's only hold-out. (Editing by Jason Szep and Paul Simao)