WASHINGTON -- The Senate's recruiting wars took an uncertain turn Tuesday, with Sen. Don Nickles' retirement sending Republicans in search of an Oklahoma replacement while Democrats urged Sen. Bob Graham to run in Florida after folding his presidential bid.

"I didn't want to be a lifer" in the Senate, said Nickles, who announced plans to retire next year after four solidly conservative terms, including six years as second-ranking in the GOP leadership.

Democrats hoped openly for a different decision from Graham, a proven vote-getter in his southern state for a generation. "We can all hope that he will continue to contribute his passion, experience and expertise," Sen. Jon Corzine, D-N.J., the head of the Democratic Senatorial Campaign Committee, said Monday night after the Floridian left the presidential campaign.

Republicans hold a 51-48 majority in the Senate, with one Democratic-leaning independent. Both parties have had mixed results in their efforts at candidate recruitment in recent months.

Southern Democratic incumbents Zell Miller in Georgia; Ernest Hollings in South Carolina and John Edwards in North Carolina are retiring. All three states present Republicans with targets in a region where President Bush ran well in 2000 at the top of the ticket.

At the same time, Democrats gained an opportunity when former Gov. Tony Knowles announced he would challenge Sen. Lisa Murkowski in Alaska, and GOP Sen. Peter Fitzgerald's decision to retire gives them another chance to gain a seat.

While Republicans were cheered by the spate of southern Democratic retirements, the GOP failed to recruit first-choice challengers for Democratic incumbents in Nevada, Washington and North Dakota. Nor could Republicans persuade top choices to run in Florida or Illinois.

Even with Nickles' announcement, key decisions remain unmade, with the potential to affect the outcome of the national battle for Senate control next year.

Sen. John Breaux, D-La., has not yet announced his plans. And Republicans are leaning heavily on former Rep. John Thune to challenge Senate Democratic Leader Tom Daschle in South Dakota next fall.

The jockeying over Nickles' seat began almost instantly.

"We are confident that his Senate seat will stay in Republican hands," said Sen. George Allen, R-Va., who chairs the GOP senatorial campaign committee. Oklahoma has voted solidly Republican in recent presidential elections, and no Democrat had held a Senate seat from the state since David Boren retired in 1994.

Republican Rep. Ernest Istook, elected to the House in 1992, earlier indicated interest in running for the Senate if Nickles retired, and a spokeswoman reiterated his interest after Nickles' announcement. Republican officials also said Oklahoma City Mayor Kirk Humphreys and Lt. Gov. Mary Fallin were potential contenders.

Among Democrats, party officials said Rep. Brad Carson was likely to jump into the race, and Attorney General Drew Edmondson was also a potential challenger.

Graham has been a political institution in Florida, having served two terms as governor and three as senator, and his absence on the ballot would give Republicans a chance to compete for his seat.

Nor did Graham's statement of withdrawal from the presidential campaign sound like a retreat from public life.

"In Florida and across this great nation, I will continue to fight for a more secure America. ... We must have greater homeland security, greater economic security and greater health care security," he said.

According to Democratic sources who spoke on condition of anonymity, Daschle urged Graham several days ago to run for a new term if his presidential campaign fizzled. Daschle also has called Graham since the Monday night announcement, according to one official.

Nickles was the second-ranking Republican until term limits forced him from the post, and became chairman of the Budget Committee at the beginning of the most recent Congress.

As whip during the previous years, he often clashed behind the scenes with then-Majority Leader Trent Lott, R-Miss. And when Lott became embroiled in a racially charged controversy last December, it was Nickles who first said publicly that rank-and-file Republicans should look elsewhere for a new leader.

That set off a chain of events that led to Lott's decision to step aside and the selection of Sen. Bill Frist, R-Tenn., as the new Republican leader.