WASHINGTON (Reuters) - President Barack Obama on Monday pledged U.S. support for Spanish Prime Minister Mariano Rajoy's efforts to get Spain's economy back on track while acknowledging that the country faced "difficult challenges" amid the euro zone's debt crisis.

The White House said the two men spoke by telephone as part of Obama's ongoing discussions with European leaders on the euro zone economy. Obama has voiced concern that economic "headwinds" from Europe could undermine the fragile U.S. economic recovery as he seeks re-election in November.

Rajoy inched closer on Friday to asking for a European Union bailout for his country, but said he needed first to know what conditions would be attached and what form the rescue would take.

(Reporting By Matt Spetalnick)