WASHINGTON — The Democratic and Republican campaign committees together have spent more than $15 million on Oregon’s Senate race so far — the most the two party committees have spent on any Senate race in the country.

New campaign finance numbers from the Federal Election Commission show the Democratic campaign group has spent $10.2 million boosting Jeff Merkley, while the GOP campaign arm has spent nearly $5 million helping two-term Sen. Gordon Smith.

The Senate race is easily the most expensive election in Oregon history, with total expenditures now estimated at about $40 million and climbing.

By contrast, the 2006 governor’s race cost $14.7 million, and last year’s battle over Measure 50 to raise the tobacco tax to cover uninsured kids cost about $15 million.

Oregon is also the state where Democrats have spent the most this year — topping the $8.2 million the party has spent in the North Carolina Senate race and $5.9 million in Mississippi, the FEC said.

Oregon ranks behind three other states in spending by the GOP: New Hampshire, Minnesota and North Carolina. The party is defending Republican-held Senate seats in all four states.

The spending figures released this week do not include at least $11.1 million spent by Smith and $5.3 million spent by Merkley as of Oct. 15, nor do they include spending by the state parties or outside groups, who have entered the fray in Oregon with a vengeance.

At least $6 million has been spent on the race so far by groups such as the conservative Freedom’s Watch and U.S. Chamber Commerce, and another $3 million by Merkley-friendly groups such as labor unions and the liberal Majority Action Fund, according to the FEC and participants on both sides. Exact totals for outside spending were not available.

Unlike races for president and the House — where electronic filing is the norm — Senate campaign finance reports are filed on paper. The records on fundraising and spending are later scanned by FEC-hired employees so they can be stored and more easily analyzed.

Rebecca Fisher, a spokeswoman for the National Republican Senatorial Committee, said she was not surprised that Democrats were outpacing Republicans in the Oregon Senate race.

“What it boils down to is we have not had to prop up a weak candidate like they have,” she said Thursday. “They need to spend a record amount of money in the Senate race to try to elect a weak candidate. We don’t think it’s going to work.”

Matthew Miller, a spokesman for the Democratic Senatorial Campaign Committee, said it was misleading to focus on party spending, when outside groups such as Freedom’s Watch have targeted Oregon. Freedom’s Watch was launched by former White House officials and donors friendly to President Bush. Former Bush aide Karl Rove is a key adviser.

As an incumbent and a member of the Senate Finance Committee, Smith entered the race with a significant fundraising edge, Miller said.

“The big thing is Gordon Smith came into the year with a several million-dollar advantage, and he began immediately spending to attack Jeff Merkley before the (Democratic) primary was over” in May, Miller said. “And for all the NRSC’s complaining, Jeff Merkley now leads this race.”

Miller was referring to polls that show Merkley narrowly ahead in the closely watched race, which both parties have targeted as Democrats try to achieve a filibuster-proof 60-seat majority in the Senate.

In all, about $22 million has been spent by Smith and others on his behalf, while about $18 million has been spent on Merkley’s behalf.