WASHINGTON — Despite spending more than $300,000, frustrated House Democrats may abandon efforts to win a special election in Hawaii after quiet diplomacy failed to end a high-level party feud that threatens their prospects.

"It's an extremely difficult race, since two Democratic candidates are splitting the vote," said Rep. Chris Van Hollen of Maryland, chairman of the Democratic Congressional Campaign Committee.

"The local Democrats haven't been able to come together and resolve that, so we'll have to re-evaluate our participation."

Recent public and private polls show Republican Charles Djou ahead in a race to fill out the remaining few months in the term of former Rep. Neil Abercrombie, who left Congress earlier this year to run for governor.

Djou's rivals include former Democratic Rep. Ed Case, runner-up in the polls, and fellow Democrat Colleen Hanabusa, the state Senate president, who trails further behind in a race with more than a dozen candidates in all. The winner-take-all race is by mail ballot, which must be received by election officials by May 22.

At first glance, the political stakes involved are scant — the winner is assured of serving in Congress only until this fall's midterm elections, when all 435 House seats are on the ballot.

But the psychological impact of a Republican victory in the state where President Obama was born could be considerable. GOP officials say they are on a path to take control of the House this fall, and seize every opportunity to claim momentum.

Case served three terms in the House before giving up his seat in 2006 for an unsuccessful challenge to Sen. Daniel Akaka's re-election.

Sen. Daniel Inouye has said publicly Case did so after personally assuring him and Akaka that he was not going to challenge the senator, an account Case disputes.

Now, four years later, Inouye and Akaka are Hanabusa's most prominent supporters — and formidable obstacles not only to Case's comeback but to the Democratic Party's chances of holding a seat that has been in their hands since 1990.

Several officials said Senate Majority Leader Harry Reid, acting at the request of the White House, recently appealed to Inouye to change course, out of a fear that unless Hanabusa withdrew, Republicans would likely win the seat.

They spoke on condition of anonymity, saying they were not authorized to discuss details of the events.

A spokesman for Inouye said he was unaware of any such conversation. Akaka said in a brief interview he had not received a similar appeal.

Records on file with the Federal Election Commission show the Democratic campaign committee headed by Van Hollen has spent more than $300,000 on the race, much of it for ads critical of Djou and designed to prevent him from winning.

Democrats also have paid for automated telephone calls in which Obama urges voters to support "a Democrat."

Democrats have been hit with a series of retirements in recent months in districts that appear to be competitive for the first time in many years, including this week's announcement by Wisconsin Rep. David Obey that he will not seek re-election after more than four decades in Congress.

Additionally, the two parties are spending heavily in Pennsylvania in advance of a May 18 special election to fill out the term of the late Rep. John Murtha.