Nearly three-quarters of a century ago, Richard Blechynden, an Englishman, decided to show Americans the proper way to brew a cup of teaHe set up his tea booth at the St. Louis World's Fair in 1904 and waited for the customers. Unfortunately, the St. Louis temperature got up near 100 degrees and stayed there. Blechynden's tea was brisk but his business was not.

One day while killing time, which Blechynden was doing a lot of that summer, he took to pitching chunks of ice into his kettle of perfectly brewed tea. Absent-mindedly, he took a sip. Then a second. Hmmm. Maybe just a little more lemon and sugar. The rest, as they say, is history. In no time at all Richard Blechynden and his newly invented iced tea became the sensations of the St. Louis World's Fair.

The nice thing about the iced tea you're going to make tonight: It's even easier. Stay tunded.

The Staples: Make sure these all are on hand: garlic, sugar, oilive oil, white wine vinegar, salt, pepper, thyme, red wine, lemons, Worcestershire sauce, Dijon Mustard. Also, a half-dozen skewers for barbecuing.

The Shopping List: 2 pounds fresh spinach; 1/2 pound bacon; a leg of lamb, boned (approximately 7 pounds before boning); 7 large onions; 6 green peppers; 1 pound large mushrooms; 1 pound cherry tomatoes; 1 small tin of tea leaves (not tea bags); nectarines.

Prepare the Day Before: The marinade for the lamb. Mix 1 cup of red wine with 1/2 cup of olive oil and 3/4 cup of lemon juice. Add 1 onion, chopped fine. And 3 minced garlic cloves, a large pinch of thyme and a generous amount of salt and pepper.

Cut the lamb into 2-inch cubes and soak the cubes in the marinade overnight. Several times during the course of the next 24 hours, turn the meat pieces over.

Also to Be Prepared the Day Before: The iced tea. The very notion of instant iced tea is a comment on our times. What could be more instant than plain, old-fashioned, regular tea-just add boiling water right? Still this isn't enough for an Instant Culture so all-encompassing as our own. We had to find a way to make instant tea even more instant-never mind that it requires the addition of "flavor enhancers," preservatives, additives and other ingredients better suited to a laboratory.

One perfectly acceptable way to make iced tea, of course, is to brew a cup of regular hot tea and add ice-the original Richard Blechynden formula. However, since this is clearly too much work for most of us, here's a simpler method. The only catch: It must be made a day before you drink it.

Begin with a quart of cold water. Add 5 heaping teaspoons of tea leaves. Put this in the refrigerator and wait. That's all there is to it. No cooking. No muss, no fuss, no bother.

And now, on to the feast.

5 p.m.: Begin the barbecue fire.

Cut the green peppers into sqaure pieces and the onions into wedges. Cut the caps away from the mushroom stems. Thread the food on the skewers-alternating the meat chucks with the peppers, the onions, the whole mushrooms and an occasional cherry tomato thrown in for color. Set aside until later.

5:30 p.m.: For your salad you'll want spinach that is young and tender. The spinach must be carefully rinsed in a bowl of cool water, then dried with paper towels. Break the spinach leaves into small pieces. Mince one of the onions and add it to the spinach. Slice several of the raw mushrooms and add them. In future spinach salads, you may want to try adding crumbled hard-boiled egg or croutons.

Cut the bacon into small pieces and fry over medium heat until cooked through. Add 1 tablespoon of Dijon mustard and a dash of Worchestershire sauce and 1/4 cup of white wine vinegar. Mix well and set aside until ready to serve.

6 p.m.: Barbecue the skewers over the hot charcoals, turning them frequently and basting occasionally with the marinade. The trick is to have everything barbecued perfectly at ht same time-the lamb should be browned on the outside, pink and succulent on the inside; the vegetables should be cooked but not burned. Lots of luck.

When the shish kebab is done, set the skewers to the side of the barbecue and dash back into the kitchen. Heat the bacon and vinegar over high heat until the mix starts to bubble; stir it and pour it immediately along with the shish kebab.

And finally, the tea. Take your pitcher of tea from the refrigerator. Add some lemon and sugar and serve over ice cubes. You may have some trouble convincing the younger members of the family that this really is iced tea. But when you see the expressions on their faces, you'll have some inkling of what Richard Blechynden felt 74 years ago on that day when he knew the enterprise was saved.