WASHINGTON (AP) — Under pressure from fellow Democrats, the chairman of the Senate Finance Committee endorsed additional measures to defray the cost of insurance for working class families on Tuesday as the panel opened debate on sweeping health care legislation.

Aides said the changes announced by Sen. Max Baucus, D-Mont., would commit an additional $50 billion over a decade to making insurance more affordable.

The change was one of several Baucus outlined in legislation he said gave Congress “an opportunity to make history” after generations of failed attempts to overhaul the health care system.

“Let us do our part to make quality, affordable health care available to all Americans,” he said.

But Sen. Jon Kyl, R-Ariz., attacked the legislation as a “stunning assault on our liberty,” citing several provisions to strengthen the government’s role in health care.

Baucus convened the committee after months of bipartisan negotiations that failed to produce agreement on a compromise measure, although he held out hope that Sen. Olympia Snowe, R-Maine, would eventually announce her support.

Baucus’ list of changes included several sought by Snowe as well as Democrats.The chairman announced he was revising his bill to increase the subsidies going to families with incomes of up to 400 percent of poverty.

Baucus also exempted policies sold to workers in high-risk fields from a proposed excise tax. At the same time, to recover some of the revenue that would be lost, he proposed raising the tax from 35 percent to 40 percent.

Additionally, Baucus called for a stricter limit on the additional charges that insurance companies may impose on older consumers seeking coverage.

On another point, he scaled back a proposed penalty on families who defy a requirement to purchase insurance, dropping them from a maximum of $3,800 to $1,900.

Baucus’ legislation is designed to make coverage more available and affordable, at the same time it restrains the growth in the cost of medical care generally.

Its 10-year price tag is below $900 billion, according to the Congressional Budget Office.Baucus made numerous concessions to Republicans in his unsuccessful stab at bipartisan compromise, jettisoning calls for the government to sell insurance in competition with private industry, as well as a proposed requirement for large companies to offer insurance to their workers.

In his opening remarks, Baucus sought to pre-empt Republican criticism.”Despite what some may say, this is no ‘government takeover’ of health care,” Baucus said.

“Our plan does not include a public option. We did not include an employer mandate. And we have paid for every cent.”

But Sen. Chuck Grassley of Iowa, the panel’s ranking Republican, said the White House and Democratic leaders short-circuited the bipartisan talks by imposing a mid-September deadline.

“I find it utterly and completely appalling,” he said.

Grassley criticized many of the plan’s key components, from a requirement that all Americans get insurance, to the taxes that would pay for subsidies to make the coverage affordable.

He also said the bill falls short in guaranteeing that illegal immigrants won’t get government help to buy insurance, as well as in preventing funding for abortion.

The Finance Committee is the last of five panels to have a say before the full Senate debates legislation.

Senators have filed 564 amendments, some of which would make major changes to Baucus’ carefully crafted framework.

The Baucus plan would extend coverage to about 29 million Americans who lack it now, and end onerous insurance company practices, such as charging higher premiums for women and denying coverage to people in poor health.

It would make almost everyone buy insurance or pay a fee, while expanding Medicaid to cover more low-income people and providing subsidies to many in the middle class.

It would create new online exchanges where small businesses and people without government or employer-provided insurance could shop for plans and compare prices.A number of committee Democrats had raised concerns about whether subsidies in Baucus’ bill are generous enough to make insurance truly affordable for low-income people.

There also are worries about a new tax on high-cost insurance plans, which critics fear would hit some middle-class workers, including many union members in risky occupations such as mining and police work.

Those concerns were shared by Snowe, whose support could become even more critical if legislation makes it to the Senate floor, where Democrats likely will need 60 votes to pass the bill.

• David Espo and Erica Werner