WASHINGTON (Reuters) - The outside fundraising group supporting presumptive Republican presidential nominee Mitt Romney relied on a familiar ally for its largest donation in July - Houston-based home builder Bob Perry.

Perry gave $2 million to the pro-Romney "super" political action committee (PAC) Restore Our Future, bringing to $8 million his total contributions to the fund this campaign season, according to Federal Election Commission documents released on Monday.

That made Perry, who has also given $4.5 million to Republican-aligned Super PAC American Crossroads, the top Republican donor in July. Perry, a major financier of the "swift boat" campaign that attacked Democratic presidential candidate John Kerry's military record in the 2004 election, is one of the top donors to super PACs this election cycle as Republicans try to unseat Democratic President Barack Obama in the November 6 election.

Casino magnate Sheldon Adelson, who along with members of his family have given the most to Republicans in this presidential season, did not donate to Republican super PACs in July.

The pro-Romney super PAC received a $1 million donation from Renco Group Inc, owned by New York billionaire Ira Rennert, another frequent contributor to Republicans this year.

The super PACs, which are officially barred from coordinating with the candidates' campaigns, can raise and spend unlimited funds and almost exclusively invest in advertising.

Restore Our Future spent $7.2 million on an 11-state television ad campaign through August 9, highlighting Romney's work as head of the 2002 Salt Lake City Winter Olympics.

In July, Restore Our Future raised $7.5 million and spent $8.2 million, election commission filings show.

The Super PAC American Crossroads, which was co-founded by President George W. Bush's strategist Karl Rove, raised $7.1 million in July and spent $9.1 million. The group has vowed to spend $200 million on defeating Obama.

TRT Holdings Inc, a privately held Texas company that owns Omni Hotels & Resorts and Gold's Gym International, gave $1 million to Crossroads in July. Robert Rowling, chairman of TRT Holdings, contributed $1 million of his own money to Crossroads.

Both Rowling and his company have already given $1 million each.

Rove's Super PAC scooped up a $1 million donation from Robert Mercer, co-CEO of hedge fund Renaissance Technologies. Mercer previously gave $1 million to the pro-Romney Super PAC.

Stephens Inc, a Little Rock, Arkansas, broker dealer, gave Crossroads $1 million. Indiana-based Weaver Holdings contributed $1 million in July.

(Additional reporting by Alina Selyukh)