* House Majority PAC airms to win back House for Democrats
* Democrats will need net gain of 25 seats to take it back
* Democratic Super PACs lag Republican counterparts in funds
By Alina Selyukh and Alexander Cohen
WASHINGTON, May 24 (Reuters) - House Majority PAC, a "Super PAC" aimed at helping elect Democrats to the U.S. House of Representatives, raised $1.1 million in the past six weeks, according to disclosure documents released on Thursday.
The "super" political action committee had $1.9 million left in cash on hand by May 16, the filing with the Federal Election Commission showed. The group reports its financials once every quarter but the latest filing was required because of its activity in California, which has a primary on June 5.
In the first three months of the year, House Majority PAC raised $1.5 million, largely from labor unions, and had $1.7 million in cash on hand.
Since March, the group received another $115,000 from the American Federation of State, County and Municipal Employees.
Texas personal injury lawyer Amber Anderson gave $500,000 and hedge fund manager Donald Sussman doubled his earlier donation of $250,000, bringing his total donations to the group to $650,000. Stephen Silberstein, founder of library automation firm Innovative Interfaces, gave $200,000.
House Majority PAC is part of an alliance of outside Democratic spending groups formed to help the party withstand a multimillion-dollar offensive planned by their Republican counterparts.
Republican groups, vowing to pour hundreds of millions into the races, hope to unseat Democratic President Barack Obama in the White House, keep the Republican majority in the House and take control of the U.S. Senate.
California has 13 competitive races, according to the Cook Political Report. House Majority has reported spending $568,936 in the state's seventh and 26th districts, two races currently held by Republicans but rated as a toss-up by the Cook report.
Democrats need a net gain of 25 seats to become the majority party in the House.
House Majority PAC, like any other Super PAC, can raise and spend unlimited money to help Democratic candidates or attack rivals as long as it does not coordinate with official campaigns or party efforts.
The Democratic Congressional Campaign Committee, the House-focused fundraising arm of the national party, last week said it raised $6.5 million in April and had $25 million in cash on hand - just behind its Republican counterpart.
Democratic Super PACs for their part have been badly trailing their Republican rivals as many Democrats remain staunchly opposed to the very notion, spawned by a 2010 Supreme Court that removed limits on how much corporations, unions and other outside groups could spend on helping politicians.
Many wealthy Democrats' disdain for the court ruling - along with their dismay at the barrage of PAC-funded attack ads that fed into the bitter campaign for the Republican presidential nomination - put Democrats behind fundraising for PACs.
Leaders of Democratic PACs have said that donors are beginning to step up their giving as the urgency of the Senate and House races builds up.