CAPITOL — As Joseph Bruno announced Tuesday that he is stepping down as Senate majority leader, he endorsed Roy McDonald as his successor in the 43rd Senate District.

But Rensselaer County Executive Kathy Jimino said later that she is considering challenging McDonald in a Republican primary.

A potential new Democratic candidate also emerged. Michael Russo, district director for U.S. Rep. Kirsten Gillibrand, said he may challenge Brian Premo, the endorsed Democratic candidate, in a primary.

Bruno was succeeded as majority leader by his fellow Republican, Sen. Dean Skelos of Rockville Centre, Long Island. Skelos was chosen by Republican senators in a closed-door conference, then elected by voice vote on the Senate floor. His term runs until the end of this year.

McDonald, who lives in the town of Saratoga, is a Republican assemblyman with strong support in the Saratoga County Republican Committee. His candidacy also is supported by Assembly Minority Leader James Tedisco, R-Schenectady, and Sen. Hugh Farley, R-Niskayuna.

Rensselaer County Republican Chairman Jack Casey also is supporting McDonald, even though Jimino is the Rensselaer County executive. Casey said he is following Bruno’s lead, and noted that McDonald has roots in Troy. Casey, a lawyer, also works as parliamentarian for the state Senate.

McDonald’s 112th Assembly District, including all of Washington and parts of Saratoga and Rensselaer counties, has 39,373 enrolled Republicans and 21,712 Democrats. Joshua Fitzpatrick, spokesman for the Republican Assembly Campaign Committee, said there are four potential GOP candidates to succeed McDonald. They are: Rensselaer County Legislator Stan Brownell, Northumberland town Supervisor Bill Peck, Washington County Republican Chairman Mike Bittel and state Republican Committeeman Michael Dennis.

The 43rd Senate District has 77,258 enrolled Republicans and 58,856 Democrats.

Other Senate Republicans, including Farley, said they are definitely running for re-election this year. Farley described Bruno as “my closest friend in the Senate,” and an outstanding leader. But he also said the 60-year-old Skelos will bring new energy to the Republican conference.

Skelos had served as deputy majority leader under Bruno. His election means Tedisco is the only upstate legislator among the four leaders of legislative conferences. All the statewide elected officials also come from downstate.

Both Bruno and Farley, however, noted that upstate senators still account for 20 of the 32 members of the Republican conference, meaning Skelos will have to take into account upstate interests.

At a news conference, Bruno said he felt a quarter-century younger than his 79 years, but noted that his wife Barbara died this year and that he wants to spend time with his family — which now includes a great-granddaughter.

Bruno spoke, as usual without notes, and was alone at the podium in a room packed with reporters, aides, lobbyists and fellow senators.

Life is a series of crises, he said. “You deal with it. … You stay on your feet and you get results.”

His humor was in evidence as he assured everyone that mental problems or terminal illness were not behind his decision.

He paid tribute to reporters. “You help call it like you think it is. Sometimes you’re right. But you do your best.”

He also praised political allies and sometime adversaries, including Gov. David Paterson and Assembly Speaker Sheldon Silver, D-Manhattan, but not former Gov. Eliot Spitzer, whom he compared unfavorably to Paterson.

Bruno’s voice grew thick with emotion at times, and he walked away from the podium after making his statement, embracing his old friend Farley. But then the former Army boxing champion walked back, saying: “I’m not going to duck out on questions.”

In response to one question, Bruno said his retirement has nothing to do with an FBI investigation of his private business activities that has been ongoing since 2006.

“I’ve never been accused of anything,” he said, “and don’t expect to be accused of anything because I’ve never done anything wrong.”

Bruno said he almost didn’t run for re-election two years ago, but decided he could still help his Republican conference. He expressed confidence that Republicans would remain the Senate majority after the November elections.

“When do you make a change in your life?” he asked rhetorically. “We got through a session. … Now is as good a time as any to move forward. … My life really is fulfilled.”

Bruno did not give a definitive answer when asked if he will serve out his Senate term. His departure would trim the Republicans’ already slim two-vote majority, but the Legislature is not likely to be in session for most of the rest of this year.

Bruno said that from the first day he was elected a senator in 1976, he “dreamed of becoming leader. That was a dream that came true.” Bruno became leader in January 1995.

“The Capital Region,” he said, “is the most desirable place in the whole world for high technology.” He said Advanced Micro Devices would indeed be building a computer chip factory in Luther Forest, as state leaders have been hoping. “That is done,” Bruno said.

His final words at the news conference were: “It has been some journey, some run, some ride. But I’m here to laugh with you, talk with you and say thank you, God bless you.”

Later Tuesday, Paterson paid tribute to Bruno in the Senate chamber. The governor also said he knows Skelos well from his days in the Senate, regards him as a friend and looks forward to working with him. As the evening wore on, Bruno made a farewell speech on the floor of the chamber. He also introduced the Senate resolution making Skelos majority leader, which was passed at 8:39 p.m.