The Maryland House of Delegates is scheduled to vote on same-sex marriage in a session that starts Friday at 4:30 p.m.

Following debate over amendments Friday afternoon, supporters said they are optimistic that the legislation will win approval — but said the outcome is not guaranteed.

“We’re hopeful that the bill will pass,” said Del. Maggie McIntosh (D-Baltimore), a gay lawmaker. “I think it’s fifty-fifty. I can’t tell you it’s better than that.”

Supporters of the legislation, sponsored by Gov. Martin O’Malley (D), have been scrambling for days to nail down the 71 votes needed for passage. A Democratic supporter who was hospitalized this week has complicated the counting over an emotional issue that has split the chamber.

Republican House leaders sought to postpone further debate until Monday, arguing that Democrats, who control the chamber, were muscling the issue through after repeated delays this week when they did not have sufficient votes.

House Minority Leader Anthony J. O’Donnell (R-Calvert) accused Democrats of trying to “ram it through on a Friday evening.”

“I believe everyone has had appropriate time to debate this,” said House Speaker Michael E. Busch (D-Anne Arundel).

A similar bill failed on the House floor last year after clearing the Maryland Senate.

This year, the Senate is waiting on House passage before taking up the bill. No senator has announced plans to vote differently than last year.

During debate Friday afternoon, the bill’s supporters accepted an amendment offered by Del. Tiffany T. Alston (D-Prince George’s), leading to speculation that she has been brought on board.

Alston co-sponsored the bill last year but backed off after she said she realized the strength of the opposition in her district.

Alston’s amendment would not allow gay nuptials to take place if litigation is still pending over the validity of signatures in a petition drive to repeal a same-sex marriage law. Both sides expect opponents to take advantage of a provision in the Maryland Constitution that allows voters to petition just-passed laws to the ballot.

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