WHITE DRESSES have always marked special occasions. Until the fashion tumult of the mid-1960s, graduation and wedding dresses could almost always be counted on to be white. Baptism, confirmation and communion dresses have remained white.

Now, the guest as well as the graduate is wearing white. Long white dresses with ruffled flounces, white jumpsuits, white suits for women, white tuxedo shirts and trousers and white double-breasted suits for men have become popular for many traditional warm weather occasions this year, even weddings.

There's a good reason for all the white clothes around this season. With the high price of clothes, even for warm weather, each purchase needs to be special, more than just something to wear. Though white clothes require special care, they have a striking appearance. Any color accessory, even off-white, goes with white. Many white clothes can be handwashed carefully.

Among some of the new white clothes in stores:

White cotton knit drawstring mini by Tric-Trac Ltd. from Garfinckel's ($52); Dorothe'e Bis' linen big jacket ($156) and wide-leg crop pant ($110) from Woodward & Lothrop; white lace and cotton dressy dress ($187) by Catherine 1 pour Philippe Salvet at Philippe Salvet (Georgetown Park); Norma Kamali's oversized T-shirt ($48) and full harem pant ($59) from Hecht's.