The Office of Personnel Management yesterday extended the "open season" on the Federal Employees Health Benefits Program through Dec. 23, giving federal workers more time to select health insurance coverage for 1983 from among the 131 increasingly competitive plans now offered.

OPM had initially scheduled open season--the traditional shopping around period for health insurance--for Nov. 22 through Dec. 10. It decided to extend the season by 13 days because of delays in distributing plan brochures and cost-benefit comparison information.

The federal government pays an average of about half the premiums in the health program, which covers about 400,000 federal workers and retirees here, plus their families, and about 9.2 million people nationwide. Premium costs to the workers and retirees are going up an average of 24 percent in January. Depending on the health plan, they could end up paying premiums next year ranging from $380 to $1,600. By careful shopping among the plans offered, it has been estimated that workers and retirees can save $800 or more in premium costs next year.

With cost such a factor and with so many plans, government workers are having a hard time deciding which type of coverage is best for their particular needs. Several members of Congress in the area have scheduled information seminars, beginning Monday, to help.

"The costs have gone up, and people are really scared," said Robert Honig, director of the bipartisan Federal Government Service Task Force. His office has received hundreds of telephone calls from worried federal workers and retirees, some in tears, he said, who want to save money without jeopardizing health coverage. Most employes and retirees here are eligible for between 16 and 26 of the 131 plans, including those of national carriers like Blue Cross/Blue Shield and Aetna and local health maintenance organizations and union-backed plans. Some of the major and fastest growing groups offering plans are becoming increasingly aggressive in their bids to attract new subscribers.

"It's going to be a three-ring circus in this town," said Ray Freson, public relations manager for the local Blue Cross/Blue Shield plan. His group claims nearly 72 percent of the federal enrollment in the Washington area, down from 80.5 percent of the eligible insurance market in 1979 before other carriers stepped up marketing efforts.

Blue Cross/Blue Shield is advertising its insurance plans on television and in newspapers. The Postal Mail Handlers union plan, with 300,000 persons enrolled compared to 1,100 in 1968, is handing out brochures at subway stops and is advertising its plan in radio spots and newspaper ads. The American Federation of Government Employees (AFGE) has launched a nationwide radio campaign and expects to distribute 1.5 million pieces of literature touting its plan's coverage.

For AFGE and federal unions like the National Treasury Employees Union (NTEU) and the National Federation of Federal Employees (NFFE), a good health insurance plan is an essential organizing tool. "It's the ultimate answer to the question, what good does it do to join a federal employes' union when we have to represent you anyway whether you join or not?" said Nicholas Nolan, AFGE's national secretary-treasurer.

To enroll in such a plan, federal workers must join the union offering it and pay regular dues or, if they are not at an agency represented by the union, pay an associate member fee. "It's another incentive for joining the union," says NTEU's Elaine Tager, who directs the union's health benefit plan. Enrollment has risen from 5,000 in 1980 to 19,000. NFFE has tripled its enrollment from 3,500 in 1980 to 21,500 and, like other groups, expects to pick up more members during this open season.

Federal employes may obtain more health plan information by attending the seminars scheduled for their areas. Rep. Michael D. Barnes (D-Md.) is holding one at 7:30 p.m. Monday, at the Silver Spring Armory, 925 Wayne Ave., Silver Spring. Rep. Frank R. Wolf (R-Va.) has a seminar scheduled for 7 p.m. Tuesday at George Mason High School, 7124 Leesburg Pike, Falls Church. Rep. Steny Hoyer (D-Md.) is holding an informational gathering at 7:30 p.m. Dec. 2 at Eleanor Roosevelt High School, 7601 Hanover Parkway, Greenbelt. And Sen. Paul S. Sarbanes (D-Md.) is sponsoring a seminar at 7:30 p.m. Wednesday at Poly Western High School in Baltimore.