ALBANY – Another tail could soon be wagging New York’s Republican Party.

With little fanfare, a Republican candidate for governor, William Weld, is expected to be nominated by the Libertarian Party on Saturday at its convention in Albany.

As far as minor parties go in New York, the Libertarians are on the petite side. Their enrollment of about 800 could squeeze inside your average high school cafeteria.

By endorsing Mr. Weld, a former governor of Massachusetts, the Libertarians would be making a bid to become a player in the crowded field of third parties in New York. Leaders of the party say a key aim is to use the nomination to influence Republican policy on issues like marijuana legalization, Rockefeller drug laws, and eminent domain.

Reports emerged that Mr. Weld was wooing the party’s endorsement after it became clear that he was not going to be the gubernatorial nominee of the Conservative Party, which has 154,000 enrolled members. The party’s chairman, Michael Long, has said the Conservative Party is uncomfortable with what it calls Mr. Weld’s liberal positions on social issues like abortion and gay marriage, and would be backing Republican John Faso, a former assemblyman from upstate.

Mr. Weld and the Libertarians share positions on some issues. In particular, they both favor limited government, lower taxes and spending, and protections of private property rights.

Mr. Weld rejects one of the party’s main tenets, the legalization of drugs. The Libertarian Party’s candidate in 2002 was Scott Jeffrey, who ran on a platform of legalizing marijuana and won 5,000 votes. A large fraction of New York’s Libertarians are also firmly opposed to the war in Iraq. The party put out a press release six months ago calling for a withdrawal of American troops and urging anti-war protester Cindy Sheehan to run against Senator Clinton.

“You’re not going to be lockstep on every single issue,” a spokeswoman for Mr. Weld’s campaign, Andrea Tantaros, said. Despite the differences, she said, “We’re happy to have them line up behind us.”

Running on the party’s ballot line could help Mr. Weld attract votes from New Yorkers who identify themselves as libertarian. If he is the Republican candidate, the Libertarian support could allow him to make up for what he loses by not showing up on the Conservative line. For the Libertarians, their endorsement of Mr. Weld could be the ticket to legal party status. If Mr. Weld in the November election receives at least 50,000 votes on the Libertarian line, then the party would be awarded with an automatic position on the ballot for at least the next four years.

If that happens, their endorsement would suddenly become a hot commodity. The ambition of party leaders is to use prominent ballot placement to challenge the Conservatives for the role of Republican kingmaker.

The Conservative Party has the most leverage over the Republicans among third parties. A well-known fact in New York is that no Republican statewide candidate has won without Conservative backing since 1974. It provided Governor Pataki with the margin of victory over Governor Cuomo in 1994, and it almost supplanted the Republicans as a major party in 1990, when a dean of New York University, Herbert London, barely lost to little-known economist Pierre Rinfret, who ran a disastrous campaign for the Republicans.

“The expectation is that we could replace the Conservatives in a kingmaker situation,” the party’s chairman, John Clifton, a social worker in Queens, said. He said he would like the party to use that leverage to “influence Republicans on Rockefeller and legalizing marijuana.” New York’s Rockefeller drug laws, which were adopted while Nelson Rockefeller was governor in 1973, mandate long prison sentences for those convicted of drug crimes. He said he hoped his party would follow the trajectory of the Green Party, which grew exponentially between 1998 and 2002, to about 30,000 members.

“If the Libertarians become a recognized party, it becomes another tail that will be wagging the Republican dog,” said Robert Ryan, a political operative who managed the campaign of Randy Daniels, a former New York secretary of state who dropped out of the race. Mr. Daniels has since endorsed Mr. Faso for governor.

Leaders of the state Republican and Conservative parties say they are not worried about a new kid on the block. “I don’t think most Republican elected officials would be comfortable with the endorsement of the Libertarian Party,” Mr. Long said. He said the party was “extremely liberal on most issues.”

While candidates “have to appeal to other minor parties,” the executive director of the Republican Party, Ryan Moses, said, “at the end of the day, the Republicans are going to have someone who represents our values, and that’s all we’re going to do.”

A political science professor at Syracuse University, Jeffrey Stonecash, said one potential obstacle for the Libertarian Party is that New Yorkers have less of an idea what the party stands for than they do of the Conservative Party and would therefore be less willing to pull the lever for one of its candidates.