WASHINGTON — With less than a month to go before November’s general election, outside spending in Oregon’s five congressional races remains fairly low-key.

Earlier this month, Republican Super PAC, a conservative political action committee based in Indiana, spent more than $115,000 on a television ad supporting Art Robinson, according to the Washington, D.C.-based, nonpartisan Center for Responsive Politics. Robinson, a Cave Junction biochemist who co-founded the Oregon Institute of Science and Medicine, is running against Rep. Peter DeFazio, D-Springfield, in Oregon’s 4th District in a rematch of 2010’s race.

Spending by outside groups, rather than by the candidates themselves, can be one indication that the race is viewed as competitive by the political establishment in Washington, said Russ Choma, who follows money and politics for the Center for Responsive Politics.

“It is definitely a sign that there is interest from outside the district,” he said.

This year, outside groups have spent more than $2.16 million in Oregon’s 1st District, but almost all of that was during the special election in January that saw Democrat Suzanne Bonamici defeat Republican Rob Cornilles to serve the remainder of Rep. David Wu’s term. Wu, a Democrat, resigned in August 2011 after allegations surfaced that he had made improper sexual advances on the teenage daughter of a longtime supporter.

In the post-Citizens United political landscape, groups without a prominent voice within the national party can spend money directly on behalf of candidates who support a certain position, Choma said.

In 2010, the U.S. Supreme Court ruled in the Citizens United case that certain political action committees, called super PACs, can spend unlimited sums on behalf of candidates as long as they do not coordinate directly with the campaign.

Some super PACs don’t have to disclose their donors or other funding sources.

“Some (super PACs) are definitely party affiliated, or working on the interests of the party. But there are also a few that are … independent, and representing groups that haven’t had a say in the power structure before,” he said.

In the special election to replace Wu, the Democratic Congressional Campaign Committee, the campaign arm of House Democrats, spent almost $1.32 million in support of Bonamici and in opposition to Cornilles, according to the Center for Responsive Politics’ figures.

By contrast, the National Republican Congressional Committee spent $85,000 in support of Cornilles.

The House Majority PAC, a liberal super PAC that has spent the vast majority of its almost $12 million in expenditures this election on criticizing Republicans, supported Bonamici with almost $300,000. Women Vote!, another liberal super PAC, chipped in more than $240,000.

That kind of spending, both by the party and stalwart Democratic supporters, is “a sign that you’ve got the Democratic Party leaders’ attention,” said Choma.

Since then, outside spending has been very modest in Oregon. In two of the state’s five congressional races — the 2nd and 3rd Districts, seats currently held by Reps. Greg Walden, R-Hood River, and Earl Blumenauer, D-Portland — outside groups haven’t spent a dime.

All told, the Republican Super PAC has poured almost $145,000 into Robinson’s effort to oust DeFazio, the longest-serving member of Oregon’s delegation who has been in Congress since 1987.

The Democratic Congressional Campaign Committee has spent $13,369 in the 5th District in support of Rep. Kurt Schrader, D-Canby, according to the Center for Responsive Politics.

By comparison, the highly competitive race in California’s 7th District between incumbent Rep. Dan Lungren, R-Gold River, and Democratic challenger Ami Bera has attracted more than $5.2 million in outside spending. The parties’ campaign committees account for almost $2 million of that total.

Overall, super PACs have spent more than $348 million on all elections, including the presidential race, in 2012.

The parties have spent almost $120 million, and other groups, which include corporations, unions and individuals, have spent almost $202 million.