For most of us keeping track of time is no less than an art, so why not put as much art into it as possible?

Washington's museums offer a fine, if limited, collection of desk and wall calendars. Some are so attractive as to inspire you to get organized, and they all make good gifts - especially for someone who forgot your birthday last year.

By far the most widely sold museum calendar here is the Smithsonian's engagement calendar, at all Smithsonian Institution gift shops for $4.95. It's divided by weeks, each marked by an attractive color plate representing an element from the museums' collections.

Also at Smithsonian giftshops for the same price is "The American Vision," a wall calendar with large color plates for each month that may be more attractive than functional.

Monet's "Woman With a Parasol" watches over the cover of the National Gallery's handsome 1978 wall calendar ($5), which was being snapped up on a recent Sunday. Some of the color plates on the monthly entries will be familiar to museum habitues; others are more obscure but stell well reproduced.

Once again, the Corcoran Gallery offers "Images of Woman" as its 1978 engagement calendar. Give it to hard-core feminists or latent chauvinists; the former, in particular, will relate to the fine color and black-and-white plates depicting the roles of women (again from the museum's collection). A good buy at $5.95, with entries by week.

Although the Folger Shakespeare Library and Museum does not publish its own calendar, its small but handsome giftshop has ordered one tailored to the true bibliophile. The wall calendar ($10) features Arthur Rackham's well-known color illustrations for "A Midsummer Night's Dream." Entries by month, if you can bear to turn beyond the first glorious January illustration.