Former congressman Ed Case and U.S. Rep. Mazie Hirono are tied in a hypothetical matchup in the Democratic primary for U.S. Senate, a new Hawaii Poll shows.

Case, the only declared candidate so far, took 26 percent while Hirono drew 25 percent.

Former Honolulu Mayor Mufi Hannemann had 17 percent, U.S. Rep. Colleen Hanabusa had 15 percent, and Lt. Gov. Brian Schatz had 6 percent. Eleven percent were undecided.

All five Democrats were ahead of former Gov. Linda Lingle, a potential Republican candidate, in hypothetical general election pairings.

Private polls have shown similar patterns, an early consistency that could influence whether some potential candidates opt for campaigns to replace U.S. Sen. Daniel Akaka, D-Hawaii, who will not seek re-election next year.

“I think the Hirono and Hanabusa vote is one vote. If one of those people gets into the race, rather than two, that person, I think, immediately goes into the lead of the Democratic primary,” said Dan Boylan, a retired University of Hawaii-West Oahu history professor and political analyst.

“And, obviously, the closest to them would be Case.”

If both Hirono and Hanabusa enter the race, he said, he believes the vote among traditional Democrats would split and put the moderate Case at a decided advantage.

Hannemann, who, like Case, is closer to the center politically, does poorly among traditional Democrats but could compete with Case for independents and Republican crossover votes.

It is unlikely that all five prominent Democrats would jump into the campaign, however, so measuring a full hypothetical field skews the poll results.

The poll for the Senate race was conducted by Ward Research Inc. for the Star-Advertiser and Hawaii News Now among 403 registered voters statewide who usually vote in the Democratic primary. The survey was done by telephone from May 4 to Tuesday. The margin of error was 4.9 percentage points.

Case and Hirono ran against each other in the Democratic primary for governor in 2002, when Hirono prevailed and then lost to Lingle in the general election.

Case represented rural Oahu and the neighbor islands in the 2nd Congressional District for four years before leaving for an unsuccessful primary challenge to Akaka in 2006. Hirono has served the district for the past five years.

The poll found that Case has a gap over Hirono with voters on Oahu, but that Hirono does substantially better than Case on the neighbor islands.

With the Senate race in its formative stage, many of the potential candidates look more closely at their favorable and unfavorable ratings than at the horse race to see how voters perceive them.

Hirono had the highest favorable rating at 64 percent, which was taken from a larger sample of 614 voters statewide, including Republicans and independents who said they did not plan to vote in the Democratic primary.

Schatz had the lowest favorable rating at 43 percent, but that figure was influenced by the fact that he was the least known among the potential candidates. Twenty-four percent said they had heard of him but did not know enough to have an opinion and 12 percent had never heard of him. Just 20 percent had an unfavorable opinion of the lieutenant governor, the lowest among the potential candidates.

Hannemann had the highest unfavorable rating among Democrats at 42 percent — a reflection of his lopsided loss in the Democratic primary for governor last year.

Lingle, however, fared worse. Her favorable rating was 49 percent and her unfavorable rating was 47 percent. Former congressman Charles Djou, who may look at a Senate campaign if Lingle does not run, had a 49 percent favorable rating and a 36 percent unfavorable rating.

Hirono’s stellar number, Boylan said, could be because she has a relatively low profile and has not had the local news media scrutiny or the difficult recent campaigns of some of the other potential candidates.

“In Washington, you’re out of sight and out of mind. It’s one of the great strengths of being in Washington and not in Hawaii,” Boylan said.

Case said the poll suggests Democrats will have a competitive primary. He said he feels he is in a good position given that private polls have also shown him out front.

“Certainly, I hope that whoever else among the Democrats is interested in getting in does get in as soon as possible because it’s a crucial discussion and decision and I’d like to get on with the campaign and with an open discussion with whoever my opponent is going to be,” he said.

Hirono said she was gratified by the poll results.

“It’s very humbling to see this strong support for my work on behalf of the people of Hawaii,” she said in a statement. “I take their opinions seriously and have been fighting as hard as ever to create well-paying jobs, hold big oil companies accountable for rising gas prices, protect Medicare from Republican attempts to dismantle it, and promote Hawaii’s renewable energy economy.

“I appreciate the positive response to my leadership, but I don’t take it for granted and will never stop fighting for a stronger Hawaii.”

Hannemann said he believes the poll shows he is a viable candidate should he choose to run, since he has not declared and has not been out raising money.

“I still think it’s way too early to make a decision,” he said of whether he will run for Senate or Congress. “But I’m getting a lot of encouragement to go.”

The former mayor said he is not worried about his high unfavorable rating.

“Very clearly, I’m a strong personality,” he said. “I take strong positions. Like rail. So if you’re anti-rail, you’re going to come at me.”

Hanabusa declined to comment.

“Congresswoman Hanabusa continues to work hard for the people of Hawaii in Washington, D.C., as she prepares for the 2012 election,” said Ashley Nagaoka, her spokeswoman.

Schatz also declined to comment.

Lingle said she was glad her favorable rating was higher than her unfavorable rating.

“I think that’s a good place to start when you are in my position, when nearly the entire state elected official world is against you and opposing you at all times,” she said.

Lingle said she has been living a private life and has not publicly responded to any criticism of her over the past six months, which she believes has influenced her poll numbers.

“Whereas, if you’re in the heat of a campaign, you’re going to be setting the record straight constantly,” she said. “Right now, they just sort of get to comment at will because I’m living a more private life now and not sending out a news release every time they say something or do something.”

Local Democrats have told national Democrats not to read too much into early polling that shows the former governor struggling. Many Democrats say Lingle’s message discipline, experience as a statewide campaigner, and fundraising ability would make her competitive in a race that would likely bring national attention.

The most ominous warning from the Hawaii Poll for Republicans is not the strength of any of the Democratic candidates, but the overwhelming support voters have for Hawaii-born President Barack Obama.

Obama’s job approval rating in Hawaii is 74 percent — compared with about 50 percent on the mainland — a reminder that the president will likely lift all local Democratic candidates on the ballot when he runs for re-election next year.

Lingle said she believes the political landscape next year will be heavily influenced by the economy. While Obama is popular now, there is no guarantee his job approval rating will stay so high.

“It depends on what happens between now and then with the economy, and the kind of policies that they put in place,” she said. “And I think, locally, it will have an impact, too, if taxes become so burdensome on people I think there will be a backlash against those who impose those taxes on people and on businesses.

“So I see it as wide open right now.”