HARRISBURG — Tens of thousands of Pennsylvanians will lose their weekly unemployment benefits if Congress does not extend the federally funded portion that ends Dec. 1, the state Department of Labor and Industry said.

The department estimated this week that 83,000 people will lose an average weekly benefit of about $310 in December if the federal portion expires. If nothing is done, approximately 166,000 additional people would lose their benefits in the January-through-March period, the agency said.

For now, the unemployed are eligible to receive up to 99 weeks of benefits that are capped at $564 a week. After Nov. 30, most people will exhaust their benefits more quickly and new applicants will only be able to receive 26 weeks of state benefits. At the end of September, 58,000 had exhausted their benefits as the economic recovery remained slow.

Historically, the federal government offers extended benefits until the economy is in better shape, said Mark Price, a labor economist for the union-affiliated Keystone Research Center in Harrisburg.

For instance, he said, unemployment had subsided to 7.2 percent after the 1980s recession when the federal government allowed extended benefits to expire.

“If they allow it to expire now, it’s the highest it’s ever been,” Price said Friday.

The national unemployment rate was 9.6 percent in October. In Pennsylvania, it was 8.8 percent last month, down from a quarter-century high of 9.3 percent in July.

The 99-week benefit is longer than any other offered previously, according to the National Employment Law Project. The longest prior period of federal unemployment benefit extensions was 65 weeks in the mid-1970s, the New York-based organization said.