Pivotal special elections in Pennsylvania and Hawaii will occur just four days apart in May, setting up a conundrum for Republicans eager to claim momentum heading into the 2010 midterm elections.

The potentially competitive special contests in Pennsylvania’s 12th district and Hawaii’s 1st district will be held on May 18 and 22, respectively, although the Hawaii contest presents extraordinary circumstances because it is likely to be held by mail.

The cash-strapped National Republican Congressional Committee must weigh how much to spend on each race or whether to play at all, with the big payoff being capturing two Democratic seats — and the GOP’s first competitive special election win this cycle.

House Democrats, flush with funds, will be eager to hold both seats six months before voters head to the polls in what is expected to be a difficult climate for the party.

“If you spend the money and you win, you look good. You can’t spend enough to win the seat,” said former Rep. Tom Davis (Va.), who was NRCC chairman from 1999 to 2002. “If you lose it, you look terrible.”

The stakes are high for both parties, but especially for House Republicans, who are looking to capitalize on voters’ frustration with government in general and need tangible evidence to back up their belief that the GOP is poised to make large gains in November — and possibly win back control of the House.

When Rep. Frank Lucas (R-Okla.) and former Rep. Ron Lewis (R-Ky.) won special elections in Democratic-held districts within two weeks of each other in May 1994, it was sign of things to come: Republicans went on to take back the majority in a landslide victory.

NRCC spokesman Paul Lindsay, however, played down expectations that Republicans could win one or both seats.

“Considering that one district is the birthplace of President Obama and the other gives Democrats a voter registration advantage of more than 130,000, it is not lost on anyone that we face an incredible challenge in both races,” Lindsay said. “That being said, these elections are in early stages right now and we’ll continue to monitor them as they develop.”

After spending millions on two special election defeats in New York last year, it’s an open question whether the NRCC can even afford to make such a large investment again. The NRCC spent about $897,000 in New York’s 23rd district special election, which became a fiasco and cost Republicans a seat that had been in their control for a century.

“They got a lot of criticism for spending a lot of money in New York 23, and they lost it,” Davis added.

These days, the NRCC has one-quarter of the available cash as the Democratic Congressional Campaign Committee. The NRCC ended January with $4.1 million in the bank, compared with the DCCC’s $18.3 million.

Although the Honolulu-based district typically votes overwhelmingly for Democrats, Republicans have a competitive shot in the winner-take-all contest because two well-known local Democrats — former Rep. Ed Case and state Senate President Colleen Hanabusa — are running. Honolulu City Councilman Charles Djou is the only well-known Republican running.

“Obviously the NRCC, having not won any [competitive] special elections thus far, is really interested in winning in Hawaii and of course in Pennsylvania,” Djou said. “How active are they going to be? Honestly … I don’t know.”

Local election officials have targeted May 22 for the special election to fill former Rep. Neil Abercrombie’s (D-Hawaii) seat.

“Nothing can make a powerful statement for the Republicans about the 2010 midterm elections than to send a Republican from Barack Obama’s hometown to the Congress in the special election,” Djou added.

There are several factors, however, still up in the air for both parties in both special elections.

First of all, the Hawaii special will likely be on May 22, but the date is not official yet. More importantly, Hawaii will implement mail-in ballots for the special election — a first for Congressional races in the Aloha State.

Not only does a mail-in ballot push back the election time table into early May, when ballots are mailed out, but it also completely changes the get-out-the-vote strategy for the campaigns and national parties interested in participating in the race.

In Pennsylvania, both parties have yet to settle on a nominee in the marginally Democratic district, which became vacant in February with the death of Rep. John Murtha (D). Although Democrats have a 2-to-1 registration advantage in the district, Sen. John McCain (R-Ariz.) barely carried it in the 2008 presidential race.

Local party officials will pick their nominees in the next week, but contenders are simultaneously filing to run for a full term in the regularly scheduled primary also being held on May 18.

Local Democratic leaders will choose between Murtha aide Mark Critz and former state Treasurer Barbara Hafer on March 6. Local Republicans will pick their nominee, likely a battle between 2008 GOP nominee Bill Russell and businessman Tim Burns, on March 11. National Republicans would prefer Burns as the nominee, if for no other reason than he has the ability to self-fund a good portion of his bid.

However, Democrats will likely have the edge on May 18 no matter who is the GOP nominee because the special election falls on the same day as the statewide primaries, and the party has several competitive contests on that level including the gubernatorial race.

There’s also a question of whether investing in a special election would be worthwhile for Republicans, especially in Hawaii, where Djou has a strong chance in a plurality-vote special election but would face an uphill battle in November.

In Pennsylvania, the GOP nominee might have a bigger battle to win the special election on May 18, but the candidate could fare better as an incumbent in November when the national mood is expected to be in the GOP’s favor.