More than 300,000 Washington area federal and postal workers, executives and retirees are in line for mid-summer insurance policy rebates or back pay ranging from $18 to $5,934.

For nearly 6,000 members of the Senior Executive Service, the big bucks settlements are just a matter of time.

It is up to the Office of Personnel Management to decide whether to issue the proposed multimillion-dollar rebate to Blue Cross-Blue Shield federal health insurance policyholders. OPM is under pressure from Blue Cross-Blue Shield subscribers to release the money, and under equally heavy pressure from other feds to channel the rebate into the federal health insurance program for the good of all policyholders.

Blue Cross-Blue Shield says that insurance usage is down, so it wants to give back $289 million to its 1.5 million federal workers and retirees who hold policies, plus another $465 million to the U.S. Treasury.

Many rival firms, who also participate in the giant federal health program, say the rebate plan is a public relations stunt aimed at winning Blue Cross-Blue Shield more premium-payers next year. Those companies -- and some members of Congress -- think the money would be better used to lower premiums and raise benefits next year for all of the 10 million people in the federal health program.

About half the people in the Washington area get broken legs mended, health checkups, babies delivered and teeth cleaned through the federal health program. Rebates proposed for Blue Cross-Blue Shield policyholders (about 45 percent of the total) would range from $18 for persons with single coverage to $374 for those with family plans. All payments, if approved by OPM, would be tax-free.

The second "bonus" is a sure thing, though OPM still hasn't announced when it will be paid out. It is the result of a successful court fight waged by individual members of the Senior Executive Service.

Most of the 6,000-plus members of the SES are in the Washington area. The SES has six pay levels ranging from $61,296 to $72,300. The SES won a partial court victory in its claim that Congress illegally "capped" part of the pay raises its members received during the 1979 through 1982 fiscal years. The court upheld its claim for full catch-up payments for two of those years.

Here is the SES back pay schedule:

Persons in SES pay level 3 during the 1980 will get a settlement of $1,051.50. Those in levels four, five and six will get the same payment of $2,637.50. There is no back pay due for persons in levels one and two.

Persons in the SES during fiscal 1981 will get $2,134.50 for level one, and those in levels two through six will get $2,637.50.

Anyone in the SES for the first three months of fiscal 1982 (October, November, December of 1981) will also get a flat payment of $659.38.