WASHINGTON - Advocacy groups lobbied President Obama and Congress yesterday, trying to eliminate what they called a "loophole" in Senate health-care legislation that they said could allow insurers to raise rates on customers based on their weight or blood sugar levels.

The groups said that would contradict one of the main goals of the congressional health-care overhaul, which is to eliminate insurance-company practices such as charging more or denying coverage based on health status.

The push came amid intense behind-the-scenes negotiations on Capitol Hill and at the White House to reconcile health-care legislation passed by the House and Senate into a final bill Obama could sign before his State of the Union address in early February.

Separately, Sen. Ben Nelson (D., Neb.) said yesterday that he had asked Democratic leadership to extend to all states the extra Medicaid funding promised to Nebraska in the health-care bill. The Democrat wouldn't say who he had spoken to regarding the so-called Cornhusker Kickback, but he pledged he would see to it that Nebraska did not get a special deal.

House Democrats, meanwhile, held a conference call during which a number of lawmakers vented frustration over provisions in the Senate bill they don't want to be forced to accept, most prominently a tax on high-value insurance plans that House Democrats fear could hurt middle-class workers and union members. Obama will meet with union leaders on the issue Monday, union officials said.

The so-called loophole is separate issue. It is a provision that allows employers to establish "workplace wellness" programs giving financial incentives to workers who meet certain health or fitness criteria such as maintaining body-mass or blood sugar levels.

Current law allows employers to vary costs for workers based on whether they can hit those targets by as much as 20 percent. The Senate bill would raise that to 30 percent, with the possibility of a further increase to 50 percent at the discretion of government officials.

Groups including the American Heart Association and Health Care for America Now held a conference call to argue that could create two-tier health plans in which workers who are able to hit certain fitness targets pay less, subsidized by other workers who pay more, even though some of them might not be physically able, through no fault of their own, to reach the goals.

"There could be an inclination to say, 'Let's raise everyone's costs and just lower them for the 15 percent that can meet the standards,' " said Sue Nelson, a vice president at the American Heart Association.

The Senate bill also sets up a test wellness program beginning in 2014 for individuals and small businesses who buy insurance directly from insurance companies. Most Americans under age 65 are covered through their employers.

Separate provisions in the legislation would allow insurers to charge more to people who smoke and to older people. Insurance companies generally support wellness provisions.

The wellness provision is not part of the House bill. Jim Manley, a spokesman for Senate Majority Leader Harry Reid (D., Nev.) declined comment except to say the issue would be discussed with the House and the Obama administration during discussions for a final bill.