WASHINGTON—

Republican backers of President Barack Obama's trade agenda are imploring key senators to stand by their previous votes when they revisit the issue in a showdown set for Tuesday.

Opponents meanwhile are mounting an equally emotional push to keep Obama from obtaining "fast track" authority to negotiate trade agreements with Pacific Rim countries and others.

At least 60 of the Senate's 100 members must back the measure for it to clear a procedural hurdle Tuesday and complete a near-miraculous resurrection of the White House priority. In a May 21 vote, 62 senators backed fast track, but they didn't expect it to return to their chamber.

The House revived the fast track legislation last week after Democrats initially derailed it in a complicated legislative package. Republican leaders - who support Obama on trade while most of his fellow Democrats oppose him - restructured the package and then passed the key elements, with only 28 House Democrats.

Hours before the vote, House Speaker John Boehner, R-Ohio, said the goal was to get the bills to Obama by week's end before Congress breaks for the July 4th recess "and deliver this win for the American people."