“We’re very clear that the vote on Monday electing yours truly as president pro tempore, electing Senator Skelos majority leader, should hold and will hold,” Mr. Espada said Monday evening.

Adding to the confusion, Democrats chose Senator Sampson as the leader of their caucus, a move that was a concession to Mr. Monserrate, who had insisted on the ouster of Malcolm A. Smith as majority leader. But because they no longer had the 32 votes needed to install Mr. Sampson as president of the Senate and majority leader, Democrats named Mr. Sampson “caucus leader” and left Mr. Smith as their titular leader.

“Clearly, after what happened last week, we have to make some adjustments in how we operate,” Mr. Smith said during the news conference held by Senate Democrats. “You can look at John Sampson as C.E.O.,” he added, saying that Mr. Sampson would run the caucus’s “day-to-day business.” Pressed for details of the arrangement, Mr. Smith said, “It is what it is.”

It remained unclear when the Senate would return to work and take up key issues that await them, including mayoral control of New York City’s schools and same-sex marriage.

Even if senators came back, it could be difficult to get much done. The lieutenant governor breaks ties in the Senate, but that office was left vacant when Mr. Paterson ascended to the governorship last year amid Eliot Spitzer’s prostitution scandal.

At the Democrats’ news conference, Mr. Smith looked on impassively as Mr. Monserrate saluted his “good friend John Sampson” and hailed the leadership change.

“I also want to send a message to the voters in my district, and the borough of Queens and downstate, in the neighborhoods that I grew up in throughout the city,” Mr. Monserrate said. “The voters in my district sent this ex-Marine, this ex-beat cop, to come up here and shake things up, and I’m not walking away from that.”