Office of Personnel Management soon will officially announce plans for two open seasons this year--in May and November--for federal workers and retirees who want to change health insurance coverage.

Nearly a million U.S. employes, family members and retirees in the Washington area are covered by one of 120-government backed health plans. They did not have a chance to shop for better, or cheaper, coverage this year even though premiums jumped an average 30 percent in January and many plans cut benefits.

OPM chief Donald J. Devine told the Federal Managers Association convention here yesterday that there will be a May 3-28 enrollment period for workers who wish to switch coverage for what remains of the 1982 year. Changes made in May would be effective in July.

Devine also said OPM will hold another open season in November for people who want to shop for 1983 health insurance coverage. Premiums and benefits for the 1983 program will be negotiated later this summer.

OPM canceled the November 1981 open season on grounds that there was not time to print brochures reflecting premium and benefit changes for the program that went into effect in January of this year.

OPM last year told carriers to cut benefits (to reduce government premium costs). It was tied up in court most of last year by unions and insurance carriers who protested orders to eliminate or reduce 1982 benefits for such things as abortions, treatment of alcoholism or mental illness.