DENVER (AP) — Bipartisan agreement on health care? It didn’t last long in Colorado.

A proposal to set up a state health insurance exchange, a market in which individuals and small businesses could pool together for lower premiums, seemed to go on life support Thursday even as a Senate committee approved the measure after hours of testimony from doctors, nurses and businesses supporting the idea.

The shift came after a Republican backing the exchange, House Republican Leader Amy Stephens, sent a letter to her colleagues in the Senate suggesting an amendment that could pull the plug on an exchange.

Stephens, a co-sponsor of the plan, said the exchange has been interpreted as support for the federal health care law passed last year. Because of that, Stephens said the Colorado proposal should be enacted only if the federal government gives Colorado “a full waiver from all terms, restrictions, and requirements in the federal Patient Protection and Affordability Care Act of 2010.”

If approved, Stephens’ amendment would likely mean the Colorado exchange would never get off the ground.

Stephens acknowledged in her letter that conservatives have howled over her support for an exchange. She wrote that the federal law “has so thoroughly contaminated the public discourse about the nation’s healthcare system that even simple and common-sense ideas like healthcare exchanges have become toxic and fraught with public policy peril.”

Health care exchanges are controversial because they’re required in the federal law. The overhaul says that states must set up exchanges by 2014, or the federal government will step in and create exchanges for them. Some opponents of the health care law therefore argue that exchanges are a way of complying with the federal overhaul.

“I see it as an accommodation of what Congress has tried to force the states into,” said Republican Sen. Kevin Lundberg, who voted against the bill.

Democratic supporters tried to counter that opinion in Thursday’s hearing in a Democratic-controlled Senate committee. First up to testify were a series of business groups that said they oppose the health care overhaul, but like the Colorado exchange.

“Do not allow the federal government to implement a one-size-fits-all health exchange on us,” said Tony Gagliardi, Colorado director for the National Federal of Independent Business, a major opponent of President Obama’s health care law.

The Senate committee voted on a party-line 5-4 vote not to adopt Stephens’ amendment. The Democratic sponsor of the bill, Sen. Betty Boyd, seemed a bit taken aback by Stephens’ proposal.

Boyd said that the idea seemed a last-minute suggestion, a departure from a plodding effort by Democrats and Republicans to recruit support for a state exchange.

“It’s a poison pill,” Boyd said of the amendment after the vote.

The Senate committee approved the original exchange plan, with only minimal changes. It was unclear whether the measure had any future for another Democrat-Republican agreement; Stephens was out of town on a family trip Thursday and suggested the amendment by letter.

Colorado is among the state suing the federal government over parts of the health care law, and the measure would not affect that lawsuit.

Copyright 2011 The Associated Press.