"I'm the wrong person to ask about clothes for travel," laughs Monica Mason, a senior principal dance for the Royal Ballet.

"I find I can't travel with just the minimum. I would rather take more than take less. I'm unhappy if I don't have the right thing for the right occasion. If I don't have precisely what suits my mind, I go out and buy it."

So this isn't, a typical how-to-survive-with-just-an-overnight-case-or a-seven-week-trip kind of story. It is the reality of a seven-week, hardworking, emotionally demanding kind of tour and the clothes Mason and other dancers take along, not only to be appropriately and comfortably dressed, but to feel good. And taking into consideration that this year's 50th-anniversary celebration of the Royal Ballet means more -- grander -- parties.

Mason remembers well her first store-bought clothing, given her when she was 14 by her mother (who had always made her clothes) when they came to England from South Africa.

Part of Mason's wardrobe comes from gifts she buys herself before or during the tour. "I treat myself with little things after a big performance like an opening night or a premiere."

After the debut of "Isadora" she went out and bought some Kenzo things, including the ruffled blouse and printed suit she has worn on this trip. The day after the gala opening in New York (with Mrs. Reagan present) she bought a plaid cotton sundress. She had danced Carabosse, and was doing a mime scene in the prologue of "Swan Lake" when she heard the demonstrators and soon was aware of them in the theater. "I was terribly afraid they might throw something little on stage," says Mason, who never stopped dancing during the disturbance.

In Washington this week she bought a silk print shirt and red trousers from Yves Saint Laurent at Rive Gauche.

Sundresses and other bare and lightweight clothes must be bought on the road. Hot-weather clothes simply don't exist in London, says Mason, since the weather is rarely warm enought to wear them. She packs everything else in two huge and heavy suitcases. Her dance clothes and make-up are compacted into two small carry-on cases.

She sometimes has to lug her suitcases short distances, "but usually there are some chaps around to give me a hand." Her luggage usually travels with the company wardrobe and paraphernalia, which includes washington machines, spin dryers and a 6-foot tutu pole. (About 200 Royal Ballet tutus go along on each trip.)

Company hairdressers will sometimes rescue a hairdo, smashed and possibly glue-streaked from a wig, and turn it into something special for a post-performance party. Sometimes she uses the company clothes dryer and gets an assist from the presser. But most clothes care she handles herself with a trusty traveling iron.

On one tour Mason toted a padded silk evening jacket separately in a shopping bag, and this tour colleague Genesia Rosato is carrying a sack with a huge taffeta Scarlett O'Hara dress. Mason owns a mannish-brimmed, webbed Trilby that she loves to wear, particularly in the rain, but she left that a home. "I can't bear hat boxes."

She's rarely in a dress, but in trousers and shirts or trouser suits. "They seem to suit me better.Besides I climb in and out of cars a lot, and I climb in and out of clothes, and trousers are just so easy."

The company will be traveling the day of the royal wedding. "But I've put a small British flag in my suitcase to wave on that day."