By John Whitesides

WASHINGTON (Reuters) - Republican Pat Toomey has opened a 10-point lead over Democrat Joe Sestak among likely voters in a Senate race in Pennsylvania dominated by economic worries, according to a Reuters/Ipsos poll released on Tuesday.

Toomey, a conservative former congressman, leads Sestak, a former admiral elected to Congress in 2006, by 47 percent to 37 percent barely two months before the November 2 election to replace Democrat Arlen Specter.

Toomey's lead was smaller, 40 percent to 37 percent, among a larger pool of registered voters.

Sestak's troubles are another election warning for Democrats, who face potentially big losses in the Senate and the possible loss of their majority in the House of Representatives.

Pennsylvania's high-profile Senate race is one of more than a dozen contests that could determine whether Republicans gain the 10 seats they need to regain control of the Senate and slam the brakes on President Barack Obama's legislative agenda.

Voters in Pennsylvania, a traditional political battleground state won by Obama in 2008, said they were pessimistic about the state's direction and unhappy with Democratic Governor Ed Rendell's job performance.

"This is a state that is not thrilled with the way Democrats have been performing. Republicans clearly have momentum," said Ipsos pollster Julia Clark.

A majority of voters, 55 percent, said the state was on the wrong track and only 37 percent believed it was headed in the right direction. Rendell's job performance as governor won approval from 43 percent, with 52 percent disapproving.

The struggling economy was the biggest problem on the mind of Pennsylvania voters by far, with 48 percent putting it at the top of the list over the budget deficit, which was second at 16 percent.

"People are unhappy. The economy is bad and they feel it," Clark said.

DEMOCRATIC PRIMARY FIGHT FALLOUT

The little-known Sestak beat the veteran incumbent Specter in the Democratic primary in May for the right to take on Toomey, the former head of the conservative anti-tax group Club for Growth.

Obama had endorsed Specter, but 59 percent of registered voters said Obama's backing of Specter made no difference in their decision on how to vote.

Clark said Sestak was still relatively unknown to state voters, and got off to a difficult start in the general election race after the primary battle with Specter.

"It didn't do the Democrats any good to look as disorganized as they did -- it was an image issue for them," she said of the primary.

In the governor's race, Republican Tom Corbett led Democrat Dan Onorato among likely voters by a commanding 15 points, 49 percent to 34 percent.

As in other polls, Republicans lead Democrats in their level of campaign interest and the likelihood they will vote, with 57 percent of Republicans having a great deal or quite a bit of interest in the election compared to 50 percent of Democrats.

The Ipsos poll of 600 registered voters, including 407 who said they were likely to vote, was taken on Friday through Sunday. Interviews were conducted in English and Spanish.

The full survey of registered voters had a margin of error of 4 percentage points. The smaller sample of likely voters had a margin of error of 4.9 percentage points.

(Editing by Bill Trott and Vicki Allen)