Many District Liners were surprised to learn that the United States Postal Service now wants only one address and one return address on the outside of each package.

A second address label inside the package is useful, but USPS does not want you to put more than one on the outside.

One reader to whom the address rule was news was Marion Holland of Chevy Chase, who responded with a note that said: "I am glad to be warned about addressing packages on more than one side, which is something I have often done.

"And there is something that I have always done: finished a wrapping job with good stout twine. The Post Office used to prefer it that way.

"Last month, when I handed a Christmas package across the counter at the Bethesda Post Office, the clerk pulled out a roll of wide tape and struck it down over every inch of wrapping twine. It is against the rules, she said, to put any sort of string on any package: the strings can catch in the automatic machines and gum up the works. The rule was not posted anywhere in the office and I have never seen it mentioned in print."

Good point, Marion. Let me offer some free information, no strings attached:

USPS does indeed prefer packages that do not have string outside the wrapping paper. String breaks. Knots work loose. Stray bits of twine can cause package-handling equipment to malfunction.

However, there is no rule that says a tied package is unmailable. Not yet, a least. "We don't actually forbid string," said a spokesperson. "But we do prefer tape, and appreciate it when people cooperate."

"That's the kind of friendly reply I have come to expect from The Swift Couriers," I said. "So it grieves me to tell you that I'm going to have to publish a horror story reported by another reader."

There was a small, ladylike groan from the other end. Then the spokesperson asked, sadly, "What did we do; and to whom did we do it?"

"You did it to Maripat Goggin of Reston," I said. "She has written me a very restrained report about a foul-up that would have made me a very angry.

"A week before Christmas, Mrs. Goggin sent out the last four of her Christmas cards. On the front of each envelope was a name and address, also a 15-cent postage stamp. On the back flap of each envelope was the Goggin return address. Later on that same day, all four cards were delivered to the Goggin mailbox."

"Oh, no!"

"Oh, yes, I'm sorry to say."

"And of course the postage stamps had been. . ."

"They had, indeed. The stamps had been canceled. Tom Goggin took the letters to the Post Office to see if he could at least get reimbursement for the wasted stamps, but Maripat's letter to me says the postal clerk just looked at him in astonishment."

"Oh, dear," the postal person said. "That's really inexcusable, even if the letter carrier on that day was an inexperienced part-timer helping out during the Chrismas rush. It's fundamental that the address to which a letter is to be delivered is always on the same side as the postage stamps.

"I can just picture Maripat saying, 'Doggone those people, they've made four matching envelopes to replace the ones that have already been postmarked?" And of course when we caused her to lose the 60 cents worth of postage we were really rubbing it in, weren't we? Please tell her that if something like that ever happens again she should call the Consumer Advocate office. They can't rectify every error that's made in the handling of 85 billion letters a year but they would probably apologize and refund the postage on an error of this kind."

The Consumer Advocate number is 245-4514. Some of you will probably make a note of it for future reference -- and then be unable to fine it when you need it. So let me tell you how to look it up. In the Washington phone book, look under "United States Government," then under "Postal Service US." Then, tucked in between "District of Columbia" and "Maryland," look for a subheading that says "HQ US Postal Service." You'll find the Consumer Advocate under the "HQ" subheading. It's a simple as can be, and I just don't understand why some people say they have trouble finding it. IT HURTS ONLY IF YOU LAUGH

Bob Orben says his neighborhood filling station is ready for President Carter's plan to use millions of bushels of grain to make gasohol. The station now has three pumps: "regular, premium and whole wheat."

The only problem is that the burgalar alarm on Bob's car is so sensitive. It goes off every time he pays for gas.