In the toughest, most expensive race the state has ever seen, GOP Sen. Gordon Smith and Democratic challenger Jeff Merkley were in a dead heat Wednesday, with the largest block of uncounted votes remaining in Oregon's most populous county.

PORTLAND — In the toughest, most expensive race the state has ever seen, GOP Sen. Gordon Smith and Democratic challenger Jeff Merkley were in a dead heat Wednesday, with the largest block of uncounted votes remaining in Oregon's most populous county.

With the tally of about 30 percent of the votes yet to be reported, Smith held a 9,000-vote lead over Merkley.

Still to be counted were the bulk of the votes from Multnomah County, where Merkley was expected to pick up substantial support.

The stakes are high, and the outcome of Oregon's race was being watched closely by both national parties. Democrats increased their majority in the Senate to 56 seats Tuesday, but Republicans managed to stop a complete sweep.

Oregon was one of four Senate races involving Republican incumbents that hadn't been decided.

At election night gatherings, both contenders told supporters to remain patient.

"What is apparent to us now is there will not be an ability to determine the winner tonight," Smith told a roomful of supporters Tuesday night.

Merkley made a similar point.

"Things are feeling pretty good, but it's going to take until tomorrow morning before we know for sure where this stands," he said.

Merkley was hoping to ride a Democratic wave that swept the nation. Smith, the two-term senator, ran TV ads touting his work with Barack Obama and other prominent Democrats in an effort to portray himself a political moderate.

It's been the most expensive, and at times one of the most acrimonious, Senate races in Oregon history, with both sides and groups supporting them spending millions to flood the airwaves with TV attack ads.

However, with the outcome of the race still up in the air, Smith and Merkley both sounded conciliatory tones at their Tuesday night election gatherings.

Smith acknowledged the historic nature of Obama's election Tuesday night.

"I think we should give the president-elect a round of applause," Smith said, adding a bit of personal praise to Merkley and his wife Mary for running a "great campaign."

Merkley, while noting his political differences with Smith, nonetheless praised the GOP senator's 12 years of "selfless service."

In his campaign stops around the state, Merkley tapped into an anti-GOP tide in Oregon, telling crowds that Smith was a Bush Republican who was more interested in bailing out Wall Street than helping folks on Main Street.

Merkley was helped not only by a surge in Democratic voter registration in Oregon, but also got a huge amount of help from national Democrats who early on saw Oregon as one of their best shots at knocking off an incumbent Republican.

The Democratic Senatorial Campaign Committee spent more than $10 million boosting Merkley, about twice as much as the GOP campaign arm spent helping Smith. The Senate race became the most expensive election in Oregon history, with total expenditures estimated at more than $40 million.