U.S. Senate Majority Leader Mitch McConnell (R-KY) (C) departs the Senate floor after a vote at the U.S. Capitol in Washington May 14, 2015. REUTERS/Jonathan Ernst

By Doina Chiacu

WASHINGTON (Reuters) - Top Republicans predicted on Sunday that both chambers of Congress would muster the votes to pass the "fast-track" authority sought by President Barack Obama to negotiate major trade deals, despite opposition from Obama's fellow Democrats.

"Yes, we’ll pass it. We'll pass it later this week," Senate Republican leader Mitch McConnell said in an interview with ABC.

Republican U.S. Representative Paul Ryan said on CNN's "State of the Union" that he was confident the measure would also pass the House of Representatives.

"We will have the votes," said Ryan, chairman of the House Ways and Means Committee. "We're doing very well. We're gaining a lot of steam and momentum."

The trade issue has made unlikely allies of Republicans in Congress and the Democratic president. McConnell, who has frequently clashed with Obama on a number of issues, offered him rare praise on Sunday.

"The president has done an excellent job on this," McConnell said on ABC's "This Week." He pointed out that the six-year Trade Promotion Authority was "not just for President Obama, but for the next president as well."

The Senate voted last week to consider the fast-track measure, but only after Democrats two days earlier blocked debate on the bill, which would clear the way for a 12-nation Pacific trade agreement.

Heated debate was still expected in the Senate over amendments. The measure will then move to the House, where many Democrats staunchly oppose the Trans-Pacific Partnership because they fear trade liberalization will cost U.S. jobs.

Ryan, the Republicans' 2012 vice presidential candidate, used one of Obama's frequent warnings about making sure the United States, not China, writes international trade rules.

Does the United States want other countries to adhere to American standards, Ryan asked, "versus China trying to write the rules, which degrades the standards of trade?"

Obama's aggressive defense of fast-track has put him at odds with the left wing of the Democratic Party, including Senators Elizabeth Warren, a leading liberal voice, and Bernie Sanders, who is challenging Hillary Clinton for the party's 2016 presidential nomination.

On Sunday, Sanders called on Clinton, who was an outspoken supporter of the trade pact as Obama's secretary of state, to take a stand on Obama’s deal.

"You're either for it or you're against it. No fence-sitting on this one," he said on CNN.

(Reporting by Doina Chiacu; Editing by John Whitesides and Mark Trevelyan)