The president of the nation's biggest postal union says his outfit is getting as top heavy with brass as the armed forces of some banana republics where generals practically out-number buck privates.

Actually the American Postal Workers Union has a long way to go before its 49 national, elected officers outnumberits 275,000-plus dues-paying members. But APWU President Francis S. Filbey says it may be heading that way.

In a memo to members that has rattled some APWU leaders, Filbey says the national executive board of 49 is ". . . unwieldy, overloaded, unnecessarily expensive and counterproductive." Filbey is also concerned about the officers' payroll, which now tops $1.6 million a year.

APWU got its unusually high ration of officers as the result of the 1971 merger that brought five different unions together. One of the prices of that merger was the guarantee of jobs in the new union for officers of the old unions. That happens in unions, corporations and elsewhere.

But normally, the incumbent officers are "grandfathered" in, meaning that they have the jobs as long as they can hold them, but the positions end when the incumbent dies, retires or loses a re-election bid.

However, Filbet says that at least 20 national officers have left since that merger "but not a single office has been abolished; so much for attrition."

Filbey, who is obviously not a candidate for re-election in 1978, says union members are partly to blame because their representatives at the Las Vegas convention last summer voted to add even more elective - in place of appointive - jobs.

For a lame duck, Filbey has quit a bite. He says he isn't finished with the officer issue yet.