LITTLE ROCK — Democratic U.S. Sen. Mark Pryor is locked in a tight battle against likely Republican nominee U.S. Rep. Tom Cotton, with many voters undecided more than a year before the election, according a poll released by the University of Arkansas on Wednesday.

The school's Arkansas Poll, which is conducted annually to gauge state residents' opinions about a range of issues, showed that 36 percent of people who said they were very likely to vote next year said they'd back Pryor. Thirty-seven percent said they'd back Cotton. Twenty-seven percent didn't know or refused to say. The margin of error was plus or minus 3.9 percentage points.

Pollsters completed 800 telephone surveys among a random sample of adult residents between Oct. 10 and Oct. 17. Of those, 618 identified themselves as very likely voters.

The annual poll was conducted during the 16-day federal government shutdown that ended last week with legislation that also raised the nation's borrowing limit. Pryor and Republican U.S. Sen. John Boozman both saw their approval numbers drop in the survey. The poll did not measure approval ratings for Cotton or the state's other three U.S. House members.

Pryor's approval among very likely voters dropped from 53 percent last year to 34 percent in this year's survey, while Boozman's dropped from 45 percent last year to 34 percent.

"You can see our federal figures taking it on the chin as a consequence," said Janine Parry, who directs the annual poll.

The poll, however, showed that more Arkansas voters are blaming Democrats and the White House for the shutdown than Republicans. That runs counter to national polls that have shown Republicans taking a hit politically from the budget standoff.

Thirty-nine percent of voters blamed President Barack Obama and Democrats for the government shutdown, while 27 percent blamed Republicans. Thirty-four percent blamed both parties, according to the poll.

"Arkansas proved somewhat outside the mainstream in being more likely to blame Democrats than Republicans," Parry said. "On the other hand, we're very much in the mainstream in blaming everyone in Washington, D.C., for everything."

Pryor has been identified by Republicans as the most vulnerable Senate incumbent seeking re-election next year as he seeks a third term. Cotton, who represents south Arkansas' 4th Congressional District, announced in August that he was running against Pryor.

The two have been engaged in an expensive television ad war over the past few weeks, with outside groups such as the Club for Growth and the Senate Majority PAC also running spots.

Pryor's campaign said it had long expected a tight race next year and wasn't surprised by the numbers. Campaign manager Jeff Weaver said he believed a new ad blaming Cotton for the shutdown and highlighting Pryor's work with other lawmakers to end it is helping the campaign show the difference between the two candidates.

"He's a problem solver. Tom Cotton was part of the problem," Weaver said.

Cotton's campaign welcomed the poll results.

"Arkansans are catching on," campaign manager Justin Brasell said in a statement. "Pryor says one thing in Arkansas, then does the opposite in Washington."

The survey also showed a tight race for governor, the state's other marquee ballot matchup next year, between Democratic candidate Mike Ross and Republican Asa Hutchinson. Ross is the only announced Democratic candidate, while Hutchinson is the best-known of the three announced GOP hopefuls.

Thirty-five percent of very likely voters said they'd vote for Hutchinson, while 31 percent said they'd back Ross. Thirty-four percent didn't know, refused to say or picked another candidate.

The poll also showed Democratic Gov. Mike Beebe's approval falling slightly from 72 percent last year to 68 percent this year. Beebe is term limited and can't run for re-election next year.