WASHINGTON — 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 today.

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 today 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.

Obama’s allies now are counting on the 14 Senate Democrats and 48 Republicans who supported fast track in May to do so again. Lawmakers generally dislike voting both yes and no on a contentious issue, figuring it’s better to draw the enmity of only one side.