Partisan gridlock leaves little room for serious tax legislation this election year. But the Treasury Dept.'s tax shop is looking for ways to tackle a handful of thorny but important issues. Among the items high on the agenda of Fred T. Goldberg Jr., the aggressive former head of the Internal Revenue Service recently named Assistant Secretary for tax policy: reviews of the alternative minimum tax, the tax treatment of bankruptcies and corporate restructurings, and tax rules for new financial products such as swaps. Treasury is also working to implement the "taxpayer bill of rights" enacted by Congress to curb IRS abuses. Goldberg will probably have to wait until next year for legislative solutions to most of these problems. For now, the tax chief will be happy just to get the debate under way.