The only remaining "Contract With America" proposal to have President Clinton's avowed support, the line-item veto, is ready for quick Senate approval after days of partisan wrangling. (The House version passed last month.) This afternoon, Senate Majority Leader Bob Dole dropped a plan to cut off further debate on the bill, saying he was satisfied that Democrats would quit stalling. Senate Minority Leader Tom Daschle (D-S.D.) made peace by paring 33 threatened Democratic amendments down to about a dozen.