On Nov. 10, 2014, President Obama, seated next to Singapore’s Prime Minister Lee Hsien Loong, speaks during a meeting with leaders of the Trans-Pacific Partnership countries. (Pablo Martinez Monsivais/AP)

Republicans have consistently railed at President Obama’s exercise of his executive authority, disparaging him as “an emperor” who has ignored Congress on immigration, climate and Cuba.

Now that they control both houses of Congress, those same critics are on the verge of handing the president expansive new powers to circumvent those who want to stand in his way on trade.

GOP leaders in both chambers say they are close to introducing legislation that would grant the administration broad authority to finalize the Trans-Pacific Partnership, one of the largest free-trade pacts in the nation’s history. Lawmakers would not be allowed to amend the terms, and Congress would be required to hold a relatively quick up-or-down vote that could not be filibustered.

The aim of such fast-track legislation, formally known as trade promotion authority (TPA), is to give U.S. negotiators more leverage to complete a deal by assuring their international counterparts that changes could not be made after the fact. Obama called for the powers in his State of the Union address, and his push represents a rare area of common cause with Republicans.

Though the GOP has spent the past several months accusing the president of abusing his powers by sidestepping Congress on a number of issues, only a small number of conservative law­makers have lobbied against granting Obama the additional authority on trade. Just 19 Republicans signed a letter last month warning against pursuing the fast-track legislation during the lame-duck session, and none attended a tea party group’s news conference on Capitol Hill two weeks ago to denounce the push.

“This president has earned our distrust, but having said that, I still support TPA,” Rep. Darrell Issa (R-Calif.), one of Obama’s fiercest critics as the former head of the House Oversight and Government Reform Committee, said in an interview. “I still want to have the trade team be able to go forward and make good offers.”

This week, Senate and House committees held separate hearings on the president’s trade agenda to pave the way for fast-track legislation in the next several weeks. The aim is to pass a bill through Congress by the end of March. Senate Majority Leader Mitch McConnell (R-Ky.) and House Speaker John A. Boehner (R-Ohio) support the effort.

The Obama administration hopes that expanded trade powers will help negotiators achieve a final breakthrough this year on the Trans-Pacific Partnership, a massive free-trade and regulatory agreement between the United States and 11 other countries. The deal has been hung up over a number of thorny issues — mostly between the United States and Japan on agriculture and automobiles — and U.S. officials believe they can win more concessions if other nations believe Congress has authorized the administration to put its best and final offer on the table.

Despite the tenuous alliance between the White House and the congressional GOP, the process remains uncertain. Democrats, organized labor and environmental groups have cited numerous concerns over the trade pact and warned that Congress cannot afford to relinquish any of its oversight powers on a massive deal built upon negotiations that have largely been kept hidden from public view.

GOP leaders said the real outreach on trade will be for Obama to convince skeptical members of his own party; both sides agree that a small number of Democratic votes will be needed to ensure passage of a fast-track bill. Opponents of the trade deal interrupted the Senate committee hearing Tuesday, shouting and holding signs before Sen. Orrin G. Hatch (R-Utah) ordered them removed from the room.

Last week, Rep. Sander M. Levin (Mich.), the ranking Democrat on the Ways and Means Committee, hinted that he would not now support fast-track legislation, even though he said he remains open-minded about the Pacific trade pact itself. House Minority Leader Nancy Pelosi (D-Calif.) told reporters Wednesday that she would support a fast-track bill if the administration could demonstrate that trade deals would help improve wages for American workers.

Hatch, head of the Finance Committee, has been working with Sen. Ron Wyden of Oregon, the committee’s ranking Democrat, in hopes of introducing a bipartisan measure that could gain more Democratic support.

“We will need an all-out effort by the administration to make the case for why TPA is so vital to our nation’s ability to fairly engage in international trade and to enhance the health of our economy,” Hatch said. “Simply put, trade means jobs.”

Congress established trade promotion authority in 1974 to give the president temporary powers for a defined period in hopes of bringing complicated trade deals to completion more quickly, without endless debates and pressure from interest groups.

The power was most recently granted to President George W. Bush from 2002 through 2007, and the Obama administration was able to use the fast-track provision to help close free-trade agreements with South Korea, Colombia and Panama in 2011 because the negotiations had begun during Bush’s tenure.

Last year, the White House launched a drive to renew the fast-track authority in hopes of finalizing the Pacific pact, which Obama has called a key element of his broader strategy to refocus U.S. foreign policy on Asia. But Sen. Harry M. Reid (D-Nev.), then the Senate majority leader, blocked the move amid opposition from organized labor in a midterm election year.

Under the legislation, lawmakers would be required to hold an up-or-down vote on a trade pact within 90 working days. Obama aides emphasized that could be as long as five months under the congressional calendar. “That is hardly rushing to ram something through in the dead of night,” U.S. Trade Representative Michael Froman told the U.S. Conference of Mayors last week.

In addition to the Pacific trade deal, the administration is pursuing a major trade pact with the European Union. Those talks are more nascent, but the fast-track powers would cover that deal as well, officials said.

Fast-track opponents, including many Democrats, have complained that the administration has failed to live up to promises of opening negotiations to public scrutiny. Froman’s office announced plans Tuesday to launch a new Web site to provide greater transparency.