The White House and Congressional leaders have reached a tentative deal on a proposed excise tax on high-cost, employer-sponsored insurance plans to be included in the final version of major health care legislation, according to officials familiar with the talks.

Officials did not immediately provide details of the tentative agreement, but it is expected to include an increase in the thresholds at which policies are hit by the tax.

The Senate bill currently would impose a 40 percent tax on the amount of policies for individuals above $8,500 and family plans above $23,000.

House Democrats and organized labor groups have been resisting the tax, which they say will hit many union-sponsored health plans and force an increase in medical expenses for many middle class families.

The unions have also sought changes in how the tax would be indexed to inflation, so that in future years it would not hit as many plans as quickly as it would under the Senate bill.

Congressional leaders have been careful to stress that nothing is agreed on in the health care talks until everything is agreed on. But a deal on the excise tax would be a major breakthrough.

One of the biggest differences between the House and Senate versions of the legislation is how they would pay for the nearly $1 trillion, 10-year cost. The excise tax is the biggest new revenue-raiser in the Senate bill. The House bill would impose an income surtax on individuals earning more than $500,000 and couples earning more than $1 million.