An amendment to Wall Street reform legislation to cap the size of large financial institutions could win a bipartisan majority, Sen. Sherrod Brown (D-Ohio) said Thursday.

Brown said that his and several other Democrats' proposal to limit the size of the largest banks is garnering preliminary interest from the GOP, though the Obama administration is reluctant to endorse the plan.

"We've got good support in the Democratic caucus," Brown said of his proposal on ABC's "Top Line" webcast. "We've got inquiries from the Republican side."

Brown said the proposal is likely to be offered as an amendment to the larger Wall Street reform bill once it reaches the Senate floor.

The measure would limit large banks by capping at 10 percent the share of the U.S. total insured deposits it can hold, and restrict limits on leverage.

But Brown said that the Obama administration is reluctant to get on-board with the proposal.

"Not yet, the Treasury's a little cautious on this," he said of whether he'd won administration backing. "They're emphasizing other parts of the bill at this point."

Update, 1:04 p.m.: A Senate GOP aide notes that while Brown's provision is meant to address "too big to fail" firms, the bill before the whole Senate already purports to do so, raising the prospect that a fellow Democrat might even think that Sen. Chris Dodd's (D-Conn.) bill might not address the problem.