The long-range Social Security deficit is substantially bigger than previously thought, intensifying congressional problems in forging a rescue bill, according to new estimates by the system's actuaries.

The estimates put the 75-year deficit at 2.09 percent of taxable payroll based on the law as it now stands, excluding the impact of a rescue package recommended Jan. 15 by a bipartisan presidential advisory commission.

The commission, in developing its recommendations, assumed that the deficit would be 1.8 percent of taxable payroll, which works out to several hundred billion dollars less over 75 years.

The reason for nearly half of the increase, Social Security Commissioner John A. Svahn said, is that earlier estimates did not include amounts the system will lose if the practice is continued of allowing state and local government agencies that have joined the system to opt out later.

Much of the rest of the increase results from assumption of lower birth rates in the future than previously expected.

The bipartisan rescue plan endorsed by 12 commission members recommended steps to reduce the deficit by the equivalent of 1.22 percent of taxable payroll, leaving Congress to figure out ways to eliminate what was then seen as a remaining deficit of 0.58 percent.

Five Democrats on the commission recommended a tax rise in the year 2010 to fill this gap, while eight other members favored raising the basic retirement age to 66 early in the next century. The debate on how to close the gap is expected to produce one of the major fights over the bill.

Now, with the long-run deficit estimated at 2.09 percent of the payroll, the solution may be even more difficult.

The commission's plan, including a provision to block state and local government agencies from opting out of Social Security, would eliminate 1.41 percentage points. This leaves the amount of deficit not covered by the bipartisan 12-member agreement at 0.68 percent of payroll instead of 0.58 percent.

The new long-range estimates were rushed to Capitol Hill yesterday as the House Ways and Means subcommittee on Social Security prepared to begin voting Tuesday on the rescue package.