Gov. David A. Paterson on Thursday will announce plans to introduce legislation to legalize same-sex marriage, according to people with knowledge of the governor’s plans.

Mr. Paterson’s move, which he first signaled last week after Vermont became the fourth state to allow gay and lesbian couples to wed, reflects the governor’s desire to press the issue with lawmakers in Albany as other states move ahead with efforts to grant more civil rights to homosexuals.

The action in Vermont, where state legislators overrode Gov. Jim Douglas’s veto of a bill legalizing same-sex marriage, came less than a week after the Iowa Supreme Court granted same-sex couples the right to marry.

Mr. Paterson has said in recent days that the State Legislature should move ahead now with the legislation regardless of whether it can muster enough votes. His reasoning, which some gay rights advocates have challenged, is that New York should make a statement that it is committed to treating same-sex couples the same way it treats opposite-sex couples.

The announcement will take place at 10 a.m. on Thursday at Mr. Paterson’s office in Midtown Manhattan, said people who were briefed on the governor’s plans but who asked not to be identified because they did not want to upstage the governor.

The fact that Mr. Paterson is introducing a bill does not, however, mean that action in the Legislature is imminent. It could take months — even longer — before the bill makes its way through the appropriate committees and onto the floor of the Senate and the Assembly.

“This is not a guarantee of anything,” said Assemblyman Micah Z. Kellner, a Democrat from the Upper East Side who noted that it took two months for legislation legalizing same-sex marriage to get through the Assembly in 2007 before it ultimately stalled. The Senate never acted on the bill.

The legislation is likely to have an especially bumpy ride in the Senate, where more lawmakers oppose same-sex marriage than support it. Gay rights advocates are now actively seeking more senators, both Democrats and Republicans, to vote for the bill.

While Mr. Paterson has said he would like to see lawmakers “fight it out” and debate the bill on the floor of both houses even if it fails, Albany tradition dictates that the bill is likely to come to a vote only when it has enough support to pass. Senator Thomas K. Duane, a Democrat and the bill’s chief supporter in the Senate, has said he opposes the governor’s notion of fast-tracking it. And the Senate majority leader, Malcolm A. Smith, has said he would bring the bill to the floor when it has enough support.

The same-sex bill Mr. Paterson plans to introduce is the same piece of legislation that former Gov. Eliot Spitzer introduced in 2007, said Assemblyman Daniel J. O’Donnell. The Assembly passed it by 24 votes, 85 to 61, a wider margin than expected.

Mr. O’Donnell said there was some discussion among lawmakers, gay rights lobbyists and the governor’s office about whether the legislation should include any new language that would, for example, allow city clerks to refuse to marry same-sex couples. But Mr. O’Donnell said that the decision was made to leave the bill as is.

“Whether or not the bill should be amended is a political question,” he said, “but it is a political question that would take more time than it’s worth to resolve. So we decided to leave it.”