Prospective Democratic candidates are favored over possible Republican hopefuls in an early horse race for the U.S. Senate seat being vacated next year by George V. Voinovich, a new poll shows.

But the big winner in the Quinnipiac University survey of Ohio voters is "don't know."

Lt. Gov. Lee Fisher and Secretary of State Jennifer Brunner, both Democrats, hold double-digit leads over former U.S. Rep. Rob Portman and state Auditor Mary Taylor, both Republicans.

"Ohio remains pretty blue these days, given Gov. Ted Strickland's high approval ratings in past polls and the fact that President Barack Obama carried the state easily, and it shows in the early Senate numbers," said Peter A. Brown, assistant director of the Quinnipiac University Polling Institute, in a release.

"But Republicans should not be disheartened by these numbers. We are still in the Obama honeymoon period, and both Fisher and Brunner are known almost twice as well statewide as Portman and Taylor."

Brown pointed out that more than 40 percent of independent voters, the key block that often decides elections, remain undecided.

In a possible GOP primary matchup, Portman beats Taylor 33 percent to 11 percent, with 56 percent undecided. On the Democratic side, it's Fisher with 18 percent, Brunner with 16 and U.S. Rep Tim Ryan of Niles with 14 -- and 53 percent still in the dark.

The breakdown for possible general election scenarios for the Senate seat (undecideds not included):

* Fisher 42 percent, Portman 27 percent.

* Fisher 41, Taylor 27.

* Brunner 38, Portman 28.

* Brunner 38, Taylor 26.

Brown expressed surprise that 55 percent of Ohioans did not know enough to form an opinion about Fisher, a former attorney general and 1998 candidate for governor.

"That large a number of people who can't rate Fisher is surprising and a potential problem for him if he chooses to run. He's been around so long, and just doesn't seem to have left that many footprints in the snow, in the minds of voters," said Brown.

"By comparison, Brunner, elected statewide for the first time in 2006, has almost identical favorability and unfavorability numbers to Fisher."

But 72 percent have not heard enough to form an impression about Portman, mentioned last summer as a possible running mate for Republican presidential nominee John McCain. Portman is a former U.S. trade representative and former director of the federal office of Management and Budget. He is especially unknown outside of his home Cincinnati area.

If Brunner decides to run for re-election -- as many Democrats want, since she holds a key slot on the board that will redraw Ohio legislative boundaries after the 2010 census -- she would be the early leader, the poll found. She tops former GOP House Speaker Jon Husted, now a state senator from Kettering, 42 percent to 25 percent.

The telephone poll of 1,127 Ohio voters was taken from Thursday through Monday, with a margin of sampling error of plus or minus 2.9 percentage points. The survey includes 492 Democrats, with an error margin of plus or minus 4.4 percentage points, and 374 Republicans, with an error margin of plus or minus 5.1 percentage points.

The poll is at www.quinnipiac.edu/x1322.xml?ReleaseID=1255.