Federal workers' health insurance premiums--up 56 percent in the past two years--will be heading for the roof again next year.

Some insurance insiders say that the increase could average 20 percent or more.

Right now, government employes and retirees pay $300 out of pocket for the lowest-priced health plan and up to $1,400 a year if they pick one of the more comprehensive plans.

The Office of Personnel Management is in the process of negotiating new premiums and benefits with the 100-plus carriers in the program. The new rates and benefits will be announced sometime this fall. Employes and retirees will have an open enrollment period in late November and early December when they can pick next year's health policies.

The federal health program covers one out of every two people in the Washington area. Nationwide, it provides health benefits for 10 million government workers, family members and retirees.

Currently the government picks up between 40 and 75 percent of every employe's health premiums, depending upon which plan the employe chooses.

Legislation is pending in the House to raise the federal contribution to about 75 percent of the total premium. The Senate is working on a bill that would raise the federal payment to 70 percent.

The OPM wants to go to a voucher insurance system. Under it, employes who chose low-cost basic benefit plans would have all of their premiums covered by the voucher. Workers and retirees who wanted a more costly plan would pay the difference in the premimums.

Managers of several of the government's health plans say that they anticipate an average increase of around 20 percent. The director of one union-backed plan said that he would not be suprised to see the average premium go up 25 percent, although some of the unions hope to keep their premium rise to around 10 percent.

The reason for the big anticipated jump is that health care costs are rising much, much faster than the overall cost of living.

The official increase will not be announced until September, or later. But be prepared to pay more.