(Adds Geithner comments, details)

WASHINGTON, April 29 (Reuters) - U.S. Treasury Secretary Timothy Geithner threw his support on Wednesday behind two credit card reform bills in the U.S. House of Representatives and the Senate, saying that unfair rate increases and fees should be banned.

Geithner, endorsing the "Credit Card Holders Bill of Rights" measure slated for a House vote on Thursday, said deceptive rules and practices by credit card lenders have forced Americans to pay some $15 billion a year in penalty fees.

"We need to change the rules of the game so that consumers are not caught by deceptively complex rules that allow rate hikes and penalties without notice, that hurt responsible borrowers and threaten to turn lives upside down," Geithner said after meeting with consumer groups, civil advocates and a chief sponsor of the bill, Rep. Carolyn Maloney, a New York Democrat.

"Investors crave transparency, consumers deserve the same," Geithner added.

Among other changes, the bill would eliminate retroactive interest rate hikes on existing balances and would require a 45-day notice period for any other rate increases.

The Obama administration also supports similar Senate legislation drafted by Senate Banking Committee Chairman Christopher Dodd, a Connecticut Democrat, and Sen. Carl Levin, a Michigan Democrat, the Treasury said.

Geithner said he saw the support for credit card reform in Congress as a "very strong signal of commitment to progress" on the Obama administration's financial reform agenda.

This includes much more ambitious steps, such as registration and increased disclosures for hedge funds, creating a systemic risk regulator with broad powers over large institutions and so-called "resolution authority" to seize control of large, systemically important financial firms.