In multi-employer plans, each company contributes a fixed amount that is usually based on the number of hours worked by its employees.

The reason that the 20 percent of workers in multi-employer plans benefit from the rising stock market has to do with tax law.

The generosity factor for single employer plans rose to $900 from $700, she said, while multi-employer plans increased to $1,000 from $400.

The teamsters' rank and file generally favor multi-employer plans because those who move from one trucking job to another can remain in the same plan.

"The whole purpose of multi-employer plans is to pool the risk," he said.

When a multi-employer plan has a surplus, the plan's trustees, usually representatives of labor and management, often vote to use it to increase monthly benefits.

She also said the company would make sure that the new plan's investments were managed more prudently than the teamsters' multi-employer plans.

"In the multi-employer plan, we have to pick up the slack of people who worked for other companies that went belly up."

Teamster officials are fighting to keep U.P.S. in the multi-employer plans.

The Government agency insuring workers' pensions urged Congress today to increase benefit limits on its multi-employer plan to make up for 16 years of inflation.