Voinovich, is the 4th GOP Senator all not running in 2010. Roe could be secured,

WASHINGTON (AP) -- Ohio Sen. George Voinovich has told associates he intends to retire next year rather than seek a new term, party officials said Sunday night. He is the fourth Republican to make departure plans since the Democratic landslide in November.

The officials said Voinovich intended to make a formal announcement on Monday.

They spoke on condition of anonymity, saying they were not authorized to discuss Voinovich's plans.

Voinovich spokesman Chris Paulitz on Sunday wouldn't confirm the decision. But he said a statement would be released Monday morning, and Voinovich would hold a press conference Monday afternoon.

Voinovich, 72, is one of the most popular Republican politicians in recent history in Ohio, and served as mayor of Cleveland and a two-term governor before his election to the Senate in 1998. He was considered a strong favorite for re-election if he had chosen to seek a third term in 2010.

Now, Democrats are likely to invest heavily in trying to win the seat.

In recent weeks, Sens. Kit Bond of Missouri, Mel Martinez of Florida and Sam Brownback of Kansas have all announced plans to retire in 2010. Missouri and Florida often host competitive Senate races when no incumbent is on the ballot. Kansas is more reliably Republican, although Democratic Gov. Kathleen Sebelius is a potentially strong challenger for the seat.

One Republican official said Rob Portman, a former Cabinet official in the Bush administration, is likely to seek Voinovich's seat. Portman was President George W. Bush's budget director and United States trade representative after stepping down from the House to join the administration.

Potential Democratic candidates include Lt. Gov. Lee Fisher, Ohio Attorney General Richard Cordray, Secretary of State Jennifer Brunner and Reps. Tim Ryan and Zack Space.

''If the news of Senator Voinovich's retirement is true, it would represent a real loss for the people of the Buckeye State,'' Space said in a statement Sunday night. ''His moderate and independent voice will be missed.''

Voinovich's re-election would have required him to raise millions of dollars over the next two years. His staff recently insisted that his fundraising has gone well, and that the senator has roughly $3 million already in the bank.

The November elections plunged Republicans deep into the Senate minority.

Democrats currently hold a 57-41 majority in the Senate with two vacancies. In Illinois, Democrat Roland Burris appears on track to take the place of President-elect Barack Obama, despite controversy over his appointment by Gov. Rod Blagojevich, who faces criminal charges.

In Minnesota, Democrat Al Franken holds a thin lead over former Republican Sen. Norm Coleman after a statewide recount. Coleman has filed a lawsuit challenging the results.