The State Department is up in arms at the Treasury Department because of new regulations that require Secretary of State George P. Shultz and hundreds of ambassadors and other key employes abroad to pay income taxes on the computed value of being driven to and from work. State's beef is that in most cases the U.S. diplomats are required by security considerations to be chauffeured, often along with bodyguards.

The regulations flow from the 1984 tax law, when Congress took aim at corporate "perks" such as chauffeured limousines and decreed that the value of the rides be taxed as ordinary income. State has hired legal and tax consultants to help make its case that the regs shouldn't apply to chauffeured diplomats.

State Department Comptroller Roger B. Feldman said that in Washington Shultz, Deputy Secretary of State John C. Whitehead and Chief of Protocol Selwa Roosevelt are the only senior officials driven to and from work. Abroad "hundreds" of diplomats are involved. In Bogota, Colombia, for example, everyone in the embassy is required to be taken to work in heavily guarded cars or buses, Feldman said.

State is waiting hopefully for Treasury to change its regs, at least as they apply to diplomats.

Take a Letter, Mr. Postman

The Bill Bennett Frank Speaking Award this week goes to Postmaster General Albert V. Casey, who's giving a lot of interviews since scandal erupted on the Postal Service Board of Governors two weeks ago.

Casey accepted his job early this year on the understanding that he would serve through Aug. 15, when he will assume a university teaching post. In a recent interview, he said of the arrangement: "The smartest thing I really did -- and I did it by accident, but it turned out to be brilliant -- was to announce my resignation before I announced my acceptance of the job. Immediately everybody said, 'hell, you're nothing but a lame duck, you won't be able to do anything in Washington.' Well, I view that everybody in Washington is a lame duck."

Casey also said that before he leaves he plans to recommend to his successor that the post office drop its promise of two-day delivery for first-class mail sent 60 to 600 miles, because the pledge is kept only 87 percent of the time. (Both one-day delivery, of mail traveling less than 60 miles, and three-day delivery, of mail traveling more than 600 miles, have better records, he said.)

What he'd really like to suggest, he said, is that Monday delivery of residential mail be eliminated. "I could do it," he said, "but I'm sure there'd be a court order and a law passed and everything else."

Lame ducks and sissies, too.