The Senate Finance Committee on Tuesday plunged into one of the most vigorous debates yet about its health care overhaul, arguing over whether to amend the draft proposal to add a government-run “public option.”

That option, which would be offered to uninsured individuals and small businesses along with a variety of private insurance plans, is supported by liberal but vigorously opposed by Republicans and a handful of moderate Democrats.

Two of the panel’s Democratic liberals spent the morning urging the committee to adopt a public plan in place of the consumer-owned, state-based “co-ops” that were developed by Chairman Max Baucus , D-Mont., and Kent Conrad , D-N.D.

Sen. John D. Rockefeller IV , D-W.Va., spent the morning promoting a goverment-run plan. “I don’t see any reason why we don’t do this. I can’t see why we don’t do this,” he said.

Run by the government, the plan would pay providers Medicare rates for the first two years and then set its rates by negotiation with doctors, hospitals and others.

GOP members of the committee argued that inclusion of a public plan in the exchanges, or marketplace, that the bill would create would soon lead to a government takeover of all health care.

“For most, if not all of us, on this side of the aisle . . . have long expressed misgivings about the public option,” said ranking GOP member Charles E. Grassley of Iowa. “I think it is a slow walk toward government-controlled, single-payer health care.”

Baucus is hoping to hold on to a few Democratic votes and defeat the amendment, and another, similar proposal to be offered by Sen. Charles E. Schumer , D-N.Y. Votes on both amendments were expected later in the afternoon.