Thursday’s the first “big day” for the Lieberman-Warner climate bill — the first time the bill can be officially changed, for better or worse, before the vote determining whether the full Senate Environment and Public Works Committee will consider it.

As it stands, the bill has the support of its authors, subcommittee chair Joe Lieberman (I-Conn.) and ranking member John Warner (R-Va.), plus, as announced last week, Sen. Max Baucus (D-Mon.).

That leaves four unknowns on the subcommittee that Lieberman chairs: Johnny Isakson (R-Ga.), John Barrasso (R-Wyo.), Frank Lautenberg (D-N.J.), and Bernie Sanders (I-Vt.). If they all vote no, the bill dies a quiet, unexpected death in subcommittee.

I say unexpected because the sense on the Hill right now is that the bill will move forward. One Democratic staffer told me that four no’s is not “a likely scenario.”

“It’s important for people to know that nobody’s looking for perfection” at this stage, the staffer said. What they’re looking for is evidence that some of their more fundamental concerns are addressed and that the bill doesn’t just move to the full committee exactly as introduced earlier this month.

That said, Lautenberg and Sanders are ambitious environmentalists, and their fundamental concerns are many. They’ll likely be expecting at least some strengthening of the weak emissions-credit auction, and some sharing of the extremely generous subsidies now going overwhelmingly to coal and auto industry. (Sanders wants more for clean energy.) [See this memo (PDF) from Friends of the Earth for the sheer magnitude of the proposed handouts.]

As more information comes along, I’ll pass it your way, and will provide continuing coverage on Thursday.