THE SUMMER is a great time to be a stamp collector and in Washington. Two coming events promise a good perspective on the country's postal past and a glimpse of its philatelic glamor.

On Saturday, the Smithsonian's National Museum of American History is offering a stroll down memory lane, with ZIP and without.

The museum and the Postal Service are sponsoring a special program called "Mail in Motion: The City Mail Delivery Service in America." It's a tribute to the nation's urban postal workers and how they made their appointed rounds long before ZIP codes.

There will be a folk singer to chronicle "Music in My Mailbox," songs about the mail, plus the opportunity for youngsters to learn mail-sorting techniques and a display of mailboxes.

From 10 to 4 there will be a special postmark available at the Mall entrance and free postcards designed by the museum's philatelic division. If that's not enough, there's always the national stamp collection on the third floor.

The quintessential Washington philatelic event, one that places a new stamp on center stage with the city's elite, will be staged next Friday, July 17.

That's when Anderson House, 2118 Massachusetts Ave. NW, will be the scene of a first-day ceremony for commemorative stamps being issued jointly by the United States and Morocco.

Secretary of State George P. Shultz, whose department requested the U.S. stamp, Postmaster General Preston R. Tisch and Moroccan Ambassador M'hamed Bargach are the scheduled speakers at the 7 p.m. event.

Although billed as "by invitation only," the affair is open to any stamp collector. The Postal Service insists that all first-day ceremonies be open to the public. The agency offers to supply a ticket to any collector who calls 268-2316.

And they won't have to go to Rabat to get the Moroccan stamp or have it canceled with that country's first-day markings. The Moroccan government is sending over a supply of its 1-dirham stamps on first-day covers, which the U.S. Postal Service will sell to collectors at a bargain 15 cents each, the Moroccan stamp included. The U.S. stamp will sell for 22 cents.

The new stamps, featuring a design created by Howard E. Paine of Delaplane, Virginia, will be on sale all day Friday at both the National Capital Post Office, 2 Massachusetts Ave. NE, and the 900 Brentwood Ave. NE Main Post Office. Both U.S. and Moroccan cancellations will be available at both stations, but not at the ceremony site because of space limitations.

The stamps celebrate the 200th anniversary of U.S.-Moroccan diplomatic relations. They also mark the 18th time the U.S. has issued stamps with another country.

U.S. authorities say you can expect to see many more joint issues in the future. There have been reports in the philatelic press that the U.S. next year may issue its first stamp with two other nations, accounts that are not being denied by postal spokesmen. The U.S. is said to be negotiating with Australia and Great Britain for a stamp that would mark the bicentennial of the land Down Under.

Not all of the summer stamp fun is in Washington. The Postal Service has revealed its design for the stamp to honor novelist William Faulkner, to debut August 2 in his hometown of Oxford, Mississippi.

The dark-green vertical 22-cent stamp, part of a series honoring the literary arts, was designed by Bradbury Thompson of Riverside, Connecticut. His design of a pipe- smoking Faulkner is after a portrait by Murray L. Goldsborough.

Collectors wishing first-day cancellations have until September 3 to send envelopes, with the Faulkner stamp attached, to Customer- Affixed Envelopes, William Faulkner Stamp, Postmaster, Oxford MS 38655-9991. Collectors wishing the Postal Service to affix the stamp may send personal checks for the amount of the stamps to William Faulkner Stamp, Postmaster, Oxford MS 38655-9992.

Collectors have until August 16 to request the Moroccan first-day cancellations. The address for envelopes with stamps supplied by the collector is: Customer-Affixed Envelopes, Friendship With Morocco Stamp, Washington DC 20066-9991. The address for individuals who wish to have the Postal Service affix the stamp is Friendship With Morocco Stamp, Postmaster, Washington DC 20066-9992.

The Moroccan stamp will be on sale for 12 cents from the Philatelic Sales Division, Washington DC 20265-9977 until December 31. The division is also selling the Moroccan first-day cover, but the agency requires a $5 minimum purchase and a 50-cent handling fee for mail sales.

The Postal Service will affix one U.S. and one Moroccan stamp to a single cover and cancel it with either U.S. or Moroccan devices, or both, at a price of 34 cents per envelope. The address: U.S.-Morocco Combination Covers, Philatelic Sales Division, Washington DC 20066-9994.