Federal and postal unions spent record amounts of money on this year's presidential and congressional elections, and report that eight of every 10 House and Senate candidates they backed won.

The unions all endorsed the Mondale-Ferraro ticket, and a big chunk of the multimillion dollar war chest they raised went into the Democrats' unsuccessful challenge of the Reagan-Bush ticket.

At the congressional level, however, the unions did much better. They are counting on incumbents and newcomers backed by union political action committee funds to help them fight off cuts in federal employe benefit programs -- particularly the government's retirement plan -- that will be proposed next year.

Congress will set up a new retirement system next year to cover federal workers who have been hired since January of this year. Any new system for them probably would include some form of integration of social security and civil service retirement benefits.

Unions fear that in the process of creating a retirement system for post-1983 workers, Congress and the White House also will make changes in the current civil service pension program.

If any changes are made, they are likely to include a partial reduction of cost-of-living raises for retirees, and an increase in the employe contribution to the civil service retirement package.

Insiders think there is little chance that Congress will raise the retirement age for current employes, although that will be proposed and debated.