The Administration seems on the verge of eking out slim Congressional approval of a new world trade treaty, but today, giving a last-minute bipartisan boost to the cause, President Clinton threw a White House pep rally showcasing prominent Republican and Democratic supporters. Flanked by Bush Administration Secretary of State James Baker and James Miller, Ronald Reagan's Budget Director, Clinton said theGATT agreementnot only tears down significant trade barriers, but "also bulldozes differences of party, philosophy and ideology." Driving the point home, the White House released a pro-GATT letter signed by Presidents Ford, Carter and Bush.Passage of the treaty on the House floor is expected Tuesday. But obstacles remain in the Senate, where it is opposed by Democrats like South Carolina Sen. Fritz Hollings who fear huge job losses. One important Senate hurdle is a vote needed to waive rules requiring all measures to pay for themselves for ten years. "That's the key vote," says TIME Washington correspondent Adam Zagorin, "because you need 60 votes to waive the rules. The treaty itself (which only needs a simple majority) is expected to pass." Look for the treaty to hit the Senate floor on Thursday.