Nearly one of every four federal workers switched to a different health insurance plan this year in search of better--or less expensive--coverage for themselves and their families.

Because of the extensive policy-switching (based on estimates from insurance carriers), many feds who changed plans during the November-December open season still have not received ID cards, insurance claims forms or any sort of acknowledgement from their new health plan.

The Federal Employee Health Benefits Program (FEHBP) covers nearly half the population of metro Washington. Nationwide, the FEHBP covers 9.2 million U.S. retirees, workers and family members.

Enrollment changes here were particularly high, probably because the 400,000 enrollees here got a steady stream of news on benefit and premium changes (the average premium is up 24 percent this year) during the often chaotic open enrollment period that ended just before Christmas.

Office of Personnel Management sources say they still do not have hard numbers on how many feds and retirees switched plans during the open season, which was the second one held in 1982.

But insurance carriers--both gainers and losers--say that the number of changes they have received and are processing could reach 700,000 or more, up dramatically from the May 1982 open season, when more than half a million people nationwide picked new plans.

The backlog has caused problems for many feds and retirees with medical problems who switched plans and now have no way to prove they are insured.

This is what you can do until you get ID cards and insurance claim forms from your new health plan:

Check to see that you have a copy of Health Benefits Registration Form 2809. That is the form you used to change enrollment. You should have received a copy from your personnel office if you are an active worker, or by mail if you are a retiree. If you don't have a copy of that form, your agency personnel or insurance office can supply you with one.

Federal officials say that a copy of Form 2809 will be accepted by hospitals and most doctors as proof that you are covered.

Officials say that, despite the backlog, most employes and retirees who switched plans during the open season will be getting acknowledgement from their new carrier within the next few weeks.

Big gainers during the open season, according to industry sources, were the GEHA plan out of Kansas City, Blue Cross-Blue Shield's new standard option plan, the Mail Handlers plan, Postal Supervisors and many of the Health Maintenance Organizations.