WASHINGTON (Reuters) - The Obama administration has no backup plan if the U.S. Congress fails to act on legislation that would extend certain provisions of the USA Patriot Act, a White House spokesman said on Tuesday.

"I'm not aware of any sort of plan B that exists or that is currently being contemplated," White House spokesman Josh Earnest told reporters. "It would certainly put at grave risk these programs and could risk a lapse in some of these important national security capabilities."

Legislation to extend provisions for two months have stalled in the Senate, leaving the fate of the country's domestic surveillance program uncertain before its June 1 expiration. Republican U.S. Senate Majority Leader Mitch McConnell has said the chamber will return to Washington on May 31 to consider ways to prevent the expiration.

(Reporting by Lisa Lambert and Doina Chiacu; Additional reporting by Patricia Zengerle)