With a vote in the House fast approaching, the proposed constitutional amendment to require a balanced federal budget is facing divisions among supporters that some fear could threaten its best chance of passage in years.

The proposal, a cornerstone of the Republicans’ “Contract With America,” had been widely expected to sail through Congress. But as hearings on the amendment began this week, some proamendment legislators and advocacy groups have become panicked the amendment could be shot down because of some House Republicans’ insistence that it include language requiring that federal tax increases be passed by 60 percent margins in both houses.

Such language is included in the version of the proposal that was written in the “Contract With America” and promoted by House Speaker Newt Gingrich and House Republican Whip Rep. Dick Armey. But nervous supporters worry that the tax-limiting language may drive away at least a handful of the Democrats needed to give the proposal the two-thirds support required in the Senate to pass a constitutional amendment.

“This is a killer amendment,” said Martha Phillips, executive director of the Concord Coalition, a group pushing for elimination of the deficit. “It may waste the one perfect opportunity to get this amendment.”

An aide to Sen. Paul Simon, D-Ill., co-sponsor and longtime champion of the proposal, predicted flatly that, with the tax-limiting language “the votes are just not there. There’s no question.”

The differences over the issue again illustrate the fissures that divide the more moderate Senate Republicans from their House counterparts who have been galvanized by the Republicans’ election sweep.

The balanced budget amendment now in the Senate was developed six years ago. The 44 original co-sponsors, including Majority Leader Bob Dole, gradually cobbled together a bipartisan coalition of supporters.

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