The Pension Benefit Guaranty Corp. said it took the action because Delphi Corp. of Troy, Mich.,couldn't afford to maintain its pension plans and former parent General Motors Co. said it wouldn't assume them.
Delphi, GM's former parts division, has been in bankruptcy protection since 2005.
The federal pension agency said it expected to be responsible for about $4 billion of the hourly worker plan's shortfall of nearly $4.4 billion, about $2.2 billion of $2.6 billion in underfunding for the salaried pension plan and $50 million in underfunding for four smaller plans.
Delphi's hourly pension plan covers more than 47,000 people. The company's salaried pension plan covers an additional 20,000 or more workers and retirees.
The pension agency was created by Congress in 1974 to insure participants in defined-benefit pension plans continue their pensions if their employer is in financial distress or doesn't fully pre-fund its pension obligations.
Nearly 44 million U.S. workers in more than 29,000 private-sector pension plans are protected by the agency and some 1.3 million are covered by pension plans the agency took over.