Senate Democratic leaders are trying to move ahead with a new version of their tax “extenders” bill, but the timing of a key procedural vote is unclear.

“We’re trying to find that magic combination that will get us 60 votes,” Majority Whip Richard J. Durbin, D-Ill., said Friday, referring to the supermajority needed to invoke cloture and move ahead with debate.

Finance Committee Chairman Max Baucus, D-Mont., introduced the new bill on Thursday evening. It is similar to an earlier Baucus measure and a House-passed tax bill, but starkly different from an alternative already offered by Republicans.

Unlike earlier Democratic proposals, Baucus’ latest bill contains a disaster relief package and money for the dwindling Highway Trust Fund, and it does not include a provision permitting certain deductions for lawyers. Republicans had opposed that language.

It also includes provisions intended to win over particular Republican senators, such as a proposal long championed by Pete V. Domenici, R-N.M., to require insurance companies to offer mental health coverage that is on a par with their coverage for other medical conditions. But Domenici said Friday morning that the addition of the mental health parity measure does not alter his opposition to the tax bill.

The disaster relief package is similar to one offered recently by ranking Finance Republican Charles E. Grassley of Iowa, whose state suffered from massive floods earlier this summer. But a Grassley aide said Friday that the Baucus proposal represents a starting point for a deal, not a deal itself.

Senate Republicans have resisted pairing revenue-raising offsets with extensions of existing tax breaks. They have, however, been willing to support offsets for new tax policy.

Baucus’ latest bill retains previously proposed offsets that would curtail an offshore deferred-compensation technique and delay a tax benefit for multinational corporations. It also adds a new offset that would require brokers to report their customers’ cost basis in securities transactions. That was added because part of the provision affecting multinationals is expected to be consumed by the current housing-policy bill.