The mushrooming tobacco bill has grown so unwieldy in three weeks of Senate debate that in the end any meaningful changes in the nation's smoking policy are likely to be worked out by a small group of law-makers working behind the scenes, backers of the bill say.

Proponents are pinning their hopes on a conference committee, a panel of senators and representatives who often meet behind closed doors to settle differences between legislation that comes out of both houses. The theory goes that the conferees, perhaps working alongside the White House and even the vilified tobacco industry itself, can more easily pare down the bill without the television cameras rolling.Most pieces of legislation, especially those as sweeping and complicated as the tobacco bill, wind up in conference committees where differences between House and Senate legislation are worked out. Sometimes it's a simple process, sometimes contentious.

In the end, a conference committee's work has to be approved by a majority vote of both the House and Senate to be sent to the president for signature into law. Even then, a president can veto the legislation and, in such cases, it takes a two-thirds majority in both houses to override the veto.

"We've got to go to conference," said Senate Minority Leader Tom Das-chle of South Dakota. "I believe we can make a lot of good changes in conference to bring this bill back to reality."

Any conference will be a long time coming. The Senate bill has not passed, and there is no House version yet.

Although no senator likes everything in the bill as it crawls into its fourth week of debate, election-year politics is expected to push it to passage on a final vote.

"It's all over the place now," Sen. Ernest Hollings, D-S.C., said Thursday. "It'll get cleaned up once it gets to the House and to conference."

Talk on the tobacco bill last week increasingly turned to the legislative endgame as leadership aides indicated Senate Majority Leader Trent Lott may try to cut off debate as soon as this week in preparation for a final vote.

House Speaker Newt Gingrich stepped up his criticism of the bill sponsored by Sen. John McCain, R-Ariz., saying the House instead would vote on a measure costing the industry a fraction of McCain's $516 billion price tag. The House bill will be narrowly focused on teen smoking and drug use, Gingrich said.

Some senators have complained that lawmaking by conference may not strike the delicate balance of cracking down on the tobacco industry without driving it out of business.

"We keep hearing that the problems with the bill can be fixed in conference, that a conference committee will take care of them," Sen. Bob Kerrey, D-Neb., said last week. "That is undemocratic. We should not be writing a piece of legislation as important as this one in a conference committee."

Others fear voters will hold them accountable for whatever tobacco policy comes out of a conference committee, although it may bear little resemblance to the bills they voted on earlier.

"There's a lot of apprehension about the conference committee (because) it's out of their control," said Sen. Paul Coverdell, R-Ga., an opponent of the bill. "The notion that things get left undone on something this big leaves questions in people's minds."

McCain's bill started out broadly for legislation targeted primarily at reducing teen smoking.

But for many lawmakers, the 400-page bill was not broad enough.

In a bid for more Republican votes, the Senate adopted an amendment that would grant tax cuts to millions of married couples and self-employed workers earning as much as $50,000 a year.