By Alina Selyukh

WASHINGTON (Reuters) - The Republican Party's fundraising arm working to elect its candidates to the U.S. House of Representatives raised $6.9 million in April, slightly more for the month than its Democratic counterpart.

The National Republican Congressional Committee figures released on Friday showed that the NRCC ended last month with $31.3 million left in the bank, adding about $4.2 million to the cash on hand in March. Republicans currently have a majority in the House.

The Democratic Congressional Campaign Committee raised $6.5 million and had $25 million left on hand, according to its figures due to be officially reported to the Federal Election Commission by May 20.

The DCCC highlighted last month as the best April in its history, adding that so far this campaign season the party committee raised more than $90 million.

"Despite being in the minority, the DCCC has outraised the NRCC by $9.5 million for the 2012 elections and Speaker (of the House John) Boehner's recent admission that the Republican Majority is in jeopardy has energized our grassroots supporters even more," said DCCC spokesman Jesse Ferguson.

Democrats are vying for dozens of House seats this campaign season, hoping to regain control of the lower chamber in November's elections after a painful loss to Republicans in 2010.

The NRCC highlighted that it is nearly $20 million ahead of its own fundraising by this point in the 2010 cycle as well as $4 million ahead of Democrats' fundraising at that time.

With formidable outside non-profit and Super PAC groups laying down millions to influence congressional races, national parties are preparing to spend their share on advertising and get-out-the-vote efforts.

Already, preparing for a battle over airwaves with other groups hoping to reach viewers during what is expected to be a heated presidential campaign, the DCCC has reserved more than $32 million worth of broadcast TV time for 36 races, predominantly in markets covering Republican incumbents.

The two party committees did not specify how much they spent in April, but calculations show the DCCC spent about $4.3 million and NRCC spent about $2.7 million.

In March, the DCCC raised $9.8 million and had just under $23 million left in cash on hand. The NRCC raised $9.3 million and had roughly $27 million left on hand.

Among the outside groups weighing into the congressional races is Majority PAC, a Democratic "super" political action committee helping elect its party members to the Senate.

The group has been struggling to catch up to deep-pocketed Republican groups such as American Crossroads that challenge Democrats on all campaign levels.

In April, Majority PAC received a financial boost from the American Federation of Teachers with a contribution of $300,000, according to the teachers' union PAC's filing posted on Friday.

Another labor union political committee, of the National Air Traffic Controllers Association, gave $1 million to Priorities USA Action, a Super PAC helping re-elect Democratic President Barack Obama.

Majority PAC, which reports its fundraising quarterly, in the first three months of the year raised some $1.7 million and emerged with about $2.5 million in cash on hand, according to its latest FEC filing.

Priorities USA, whose April filing is due by May 20, in March raised $2.5 million and had $5 million left on hand.

(Reporting by Alina Selyukh and Alexander Cohen; Editing by Vicki Allen and Jackie Frank)