JACKSON (AP) — Sen. Trent Lott of Mississippi, the Senate’s No. 2 Republican, plans to resign his seat by the end of the year, congressional and Bush administration officials said Monday.

Lott, 66, scheduled two news conferences in Pascagoula and Jackson later in the day to reveal his plans. According to the officials, who spoke on condition of anonymity ahead of the announcement, Lott intends to resign effective at the end of the year.

No reason for Lott’s resignation was given, but according to a congressional official, there is nothing amiss with Lott’s health. The senator has “other opportunities” he plans to pursue, the official said, without elaborating. Lott was re-elected to a fourth Senate term in 2006.

Arizona Sen. Jon Kyl, who helped broker a bipartisan immigration bill that went down to defeat this year despite President Bush’s support for it, will run to replace Lott as the Republicans’ vote-counting whip, said spokesman Ryan Patmintra.

Lott’s colleagues elected him as the Senate’s Republican whip last year, a redemption for the Mississippian after his ouster five years ago as the party’s Senate leader over remarks he made at retiring Sen. Strom Thurmond’s 100th birthday party. Lott had saluted the South Carolina senator with comments later interpreted as support for southern segregationist policies.

After the 2006 elections, when Democrats recaptured the Senate, Lott was put in charge of lining up and counting Republican votes as whip, the No. 2 job behind minority leader Mitch McConnell.

His 2006 comeback was an apt outlet for the Mississippian’s talents. He was the rare majority leader who seemed to relish the vote-wrangling duties that some of his predecessors loathed.

Lott becomes the sixth Senate Republican this year to announce retirement. Democrats effectively hold a 51-49 majority in the chamber, including two independents who align themselves with Democrats.

His retirement means that Republicans will have to defend 23 seats in next year’s election, while Democrats have only 12 seats at stake.

Mississippi’s Gov. Haley Barbour, a Republican, will appoint Lott’s temporary replacement, who will serve until the 2008 elections, when voters will elect someone to serve out the balance of Lott’s term, which runs through 2012.

Lott’s seat is likely to remain Republican. GOP Rep. Chip Pickering of Mississippi, a former Lott aide who recently announced his retirement from the House, is widely seen as a potential successor. Aides to Pickering said he would withhold comment until after Lott’s news conference.

The smooth-spoken Lott found himself in hot water in December 2002 after going too far in his praise of Thurmond at the South Carolinian’s 100th birthday party. Lott said Mississippi voters were proud to have supported Thurmond when he ran for president on a segregationist platform in 1948, and added: “If the rest of the country had followed our lead, we wouldn’t have had all these problems over all these years either.”

A few days later, Lott issued a statement saying he had made “a poor choice of words” that “conveyed to some the impression that I embraced the discarded policies of the past. Nothing could be further from the truth, and I apologize to anyone who was offended by my statement.”

But the damage was done. President Bush distanced himself from Lott’s remarks, telling an audience the comments “do not reflect the spirit of our country.”

Lott then made a round of public appearances, apologizing for his gaffe. He called his remarks “insensitive” and said he regretted “reopening old wounds and hurting so many Americans.” He also apologized on Black Entertainment Television and promised to use his position to help push through initiatives that would benefit minorities.

Lott later wrote in a book — “Herding Cats: A Life in Politics” — that President Bush hurt his feelings by disavowing the comments in a tone that was “devastating … booming and nasty.”

Another event during Lott’s exile changed his relationship with the White House: Hurricane Katrina. The massive storm devastated Lott’s home state, not to mention his oceanside home in Pascagoula. He found his refrigerator a few blocks away in a neighbor’s yard. For him, the administration’s bungled response was personal. He considered retiring.

Before his Senate job, Lott served in the House, where he worked closely with other young conservatives, including Georgia’s Newt Gingrich, and showed his party loyalty by defending President Nixon at 1974 impeachment hearings. In 1981 he became the Republican whip, responsible for vote counting and making sure members toe the party line. He served in that post until 1988 when he easily won the Senate seat vacated after 41 years by Democrat John Stennis.