THIS YEAR'S planned postal rate increase may be bad news for most people who use the mails, but it's been a bonanza for Richard Schlecht of Arlington.

Schlecht is an artist and, by the time 1988 ends, he expects to have "six, seven, maybe more" of his works featured on new stamps carrying letters across the country.

The Postal Service last week released the first of the new stamps Schlecht has illustrated for the rate increase: a three-cent stamp displaying a rear view of a Conestoga wagon.

His maroon stamp should see a lot of duty this year, especially if the Postal Rate Commission accepts the recommended three-cent increase in first-class letters to 25 cents.

Schlecht said he finished work on the wagon stamp in April and has completed several others which should be announced later in the year. The volume of stamp work he does, he said with a laugh, is one of the "real advantages of living just 10 minutes, just across the bridge" from Postal Service headquarters.

The new three-cent stamp replaces a 1983 stamp displaying a railroad handcar. Both are part of the popular transportation series of engraved stamps and are sold in coils rather than sheets.

The new stamp will debut February 29 in the town for which the wagon was named, Conestoga, Pennsylvania. Speakers at the ceremony will address the crowd at the Fire Hall on Main Street from the bed of a 16-foot Conestoga Wagon.

Schlecht, 51, who is expected at the ceremony, has been working as an artist in this area since 1960. A native of Denver who came to the capital as an Army illustrator, Schlecht says he is, perhaps, best known for the historical scenes he has painted for the National Geographic Society and National Park Service.

Washington stamp collectors may recall him as the artist to whom the Postal Service hurriedly turned in 1982 after fire destroyed the Wolf Trap Farm Park's Filene Theater in Northern Virginia and the service decided to support rebuilding efforts with a commemorative stamp.

The production timetable for that stamp gave Schlecht only two weeks in which to produce a design. "It was a bit strange," Schlecht recalled.

The key issue he faced was how to portray the amphitheater. The old one was destroyed by the fire, and the design for a new one was not complete.

Schlecht, who lives off Ridge Road in "L.A." (that's what he calls Lower Arlington), says he fudged the issue with a design that shows the park's patrons lounging on the lawn with a theater in the background.

To hear Schlecht tell it, he found it a lot easier to design the wagon stamp. "It's a nice little stamp you can really get graphic with." Others, such as the typical commemorative, "get a little painterly," he said.

In the case of the wagon stamp, the Postal Service came to him and said they wanted a stamp showing the historic wagon, used by many of the country's early 19th-century pioneers to settle the Ohio Valley.

"They were open to suggestions on how to treat the wagon, what angle you pick and so on," said the artist. He furnished a black-and-white line drawing, and the Postal Service picked the color and, of course, the rate.

Collectors who want a first-day cancellation must place the new stamp and at least 19 cents additional postage on their envelopes. They should be mailed to Customer-Affixed Envelopes, Wagon Stamps, Postmaster, Conestoga, PA 17516-9991.

The Post Service will affix four of the new stamps and one 10-cent stamp on up to 50 envelopes for individuals who send envelopes and personal checks covering the stamps to Wagon Stamps, Postmaster, Conestoga, PA 17516-9992. The deadline is March 30.

Washington will be the scene of one of the biggest stamp shows ever, the Postal Service has announced. But don't rush out for your tickets; the show won't be opening until the fall of 1989.

The service will host a major philatelic exhibition at the Washington Convention Center in connection with the 20th Congress of the Universal Postal Union. That is the international organization that sets the world's postal standards, and the 1989 meeting will be the first in 92 years held in the U.S.

The show, to be called World Stamp Expo '89, will play for three weekends in November and December and should feature displays by the world's leading stamp dealers as well as the postal agencies of many nations.

Bill McAllister is a member of The Washington Post's national staff.