Nearly 600,000 jobless Californians could run out of unemployment benefits by April unless Congress extends a series of special assistance measures that expire at the end of December, says the National Employment Law Project.

The 65 percent federal subsidy for Cobra benefits will also expire at year's end, said the Law Project and allied groups at a press conference Monday in Washington.

Law Project chief Christine Owens said that nearly half of those now enrolled in the health insurance program could lose coverage unless the Cobra subsidy is reauthorized and extended.

Unemployment benefits normally last a maximum of 26 weeks and laid-off workers typically pay for continuing their old employment-based health insurance under Cobra.

MBA BY THE BAY: See how an MBA could change your life with SFGATE's interactive directory of Bay Area programs.

But under the American Recovery and Reinvestment Act, or the Obama stimulus plan, Congress allocated $40 billion to make unemployment benefits available for up to 79 weeks, and another $25 billion to subsidize Cobra.

Lawmakers recently added up to 20 weeks of unemployment checks, for a total of 99 weeks of benefits in California.

But those provisions expire at the end of December, and the groups holding Monday's press conference said that by the end of March, about 3 million Americans are projected to exhaust their benefits as the unemployment coverage maximum reverts to 26 weeks.

Making 99 weeks of unemployment benefits available throughout 2010 would cost about $85 billion, and extending the Cobra subsidy could be another $25 billion decision, said a Capitol Hill source.

House Speaker Nancy Pelosi has said she wants to extend both programs before the end of the year. New bills H.R. 4183 and S. 2381 would address jobless benefits.