At an age when most people have less bounce to the ounce, Walter S. Mack, 83, and his associates (average age 62) are setting out to prove that old cola men never go flat.

Mack and his colleagues (boasting a combined 188 years in the cola business) are taking on Coca-Cola and Pepsi-Cola, which divide 80 percent of the cola market despite the efforts of hundreds of rivals.

Hava Cola, King Cola, Queen Cola, Broma Cola, Buster Cola, Dragon Cola, Pimlicola, Pensa Cola, Why Cola and Yes It's a Cola picked up their effervescences years ago and went home. Dozens of other brands are still bubbling, but they haven't cut into the leaders' market.

If your name isn't Coca or Pepsi, the cola business is rough. Coke even tried unsuccessfully to bar other manufacturers from using the word cola, and, after all, it wouldn't sound right to order a rum-and-buster.

There are lots of brands of cigarettes. Why are there only two colas?" Mack exclaimed in the office from which he plans to launch King-Cola next year.

"There's plenty of room for three," he says grinning, "Only I want most of the business."

You may not remember Walter S. Mack, but if you've been around even half as long as he has, you'll remember his song. In 1941 it was broadcast 296,426 times in this country alone, it was, Magazine Digest wrote in 1948, "The most famous oral trademark of all times." It went:

Pepsi-Cola hits the spot.

Twelve full ounces, that's a lot

Twice as much for a nickel, too

Pepsi-Cola is the drink for you .

King-Cola is not the first cola Mack has given his heart to. Mack, who likes Pepsi-Cola, was born in the 1890s, took over as Pepsi's president in 1938, and steered the beverage concocted by a North Carolina chemist out of the pack to clear second place.

Nor is it the first time Mack has predicted Coca-Cola can be spilled from its throne.

An ebullient Mack said in 1947 that in five years Pepsi would be outselling coke. It didn't happen. Instead, in 1950 Mack was kicked upstairs to be Pepsi's board chairman as Pepsi's surge leveled off.

The fight between Coca-Cola and us is a fundamental American struggle," Mack once said.

He doesn't do anything by halves. His office at Pepsi featured a clock in the shape of a Pepsi bottle cap, a wastebasket made from a Pepsi syrup can and a radio in a model of a bottle.

A 1950 New Yorker magazine profile of Mack reported that when his 4-year-old daughter declined a Pepsi, saying she wasn't thirsty, her 7-year-old brother said: "You don't love Daddy."

Mack denies having a "Coke complex" or any resentment against Pepsi. He just claims he's got a beter cola and a beter idea that will make it possible for King-Cola to take on Coke, which has 47 percent of the regular cola market, and Pepsi, which had 33 percent.

"Coke and Pepsi have tremendously powerful images. The Cola business is very tough and it's a long time since Mack and his colleagues have been there," said analyst Emanuel Goldman, who specializes in soft-drink companies at Sanford C. Bernstein, a brokerage house. "I'm darned if I know how King-Cola will do."

Coke has no comment on its embryonic rival, and a Pepsi spokesmand said "We wish them well," although not at the expense of Pepsi, of course.

Mack's King-Cola (which has been test-marketed in Indianapolis) does taste pretty good, according to an informal survey of non-professional cola tasters.

Mack is willing to compromise. TR FOR ADD 4-COLA . . .

"We think King-Cola is better, but if you want to be pessimistic then call it just as good as the others," he said. Some would call the taste extremely close to Pepsi, perhaps unsurprisingly since the King-Cola secret brew was made by Thomas Elmezzi, 63, who was with Pepsi foir 43 years and knew their formula.

"Yours is an entirely different formula from Coke and Pepsi," Mack says. "Once the people sample it, I know they'll love it."

As Mack sees it, people will be going into supermarkets all over America saying: "I want my King-Cola. Where the hell is it?"

They will want King-Cola because it will taste as good and be cheaper and because they'll be seeing a barrage of advertising and, perhaps, whistling a new jingle (Mack likes jingles).

King-Cola will be cheaper, Mack says, because of his better idea for distribution. The two major colas began so long ago that they established distributors for areas of the nation who would deliver the cola to each store individually.

Mack is establishing only 29 sales regions, called "kingdoms," which he is in the process of selling at an average of about $1 million each.

"If they don't sell their kingdoms, there won't be any money," analyst Goldman said. Mack said that 14 kingdoms have already been sold and he had 310 applications from which to choose the 29 winners. The process of selling kingdoms will be finished by Dec. 15, he predicted.

In each kingdom, King-Cola will be delivered in solid truckload to supermarket warehouses, and the chains will take the cola into the individual stores, as Mack plans it.

In New York City, Mack said, it costs Pepsi and Coke about $1 per case to get their cola into the stores, Mack said.

As a result he says that when King-Cola goes on the market next spring, a six-pack of 12-ounce cans will cost $1.19 in New York where Coke and Pepsi six packs sell for between $1.69 and $1.89.

"That," said Mack in one of his few mentions of non-cola commodities, "will enable the housewife to buy another quart of milk or loaf of bread for her family." (The Mack family budgets for cola first, bread and milk second.)

Coke and Pepsi cannot change their systems, Mack said, because the distributors are making so much money they won't sell out except at enormous prices. "There isn't enough money in the world to buy them all back," he said.

Mack's first goal is to capture two percent of the cola market if King-Cola's first year. That would mean selling 60 million cases, or 1.44 billion 12-ounce cans. By the time he's 90, Mack says, he'll have King-Cola vying for the lead in the U.S. market, where two billion cases of regular cola are drunk every year.

"I'm going to switch them over," Mack said as he played a tape of his King-Cola jingle.

King-Cola's ads will name the cola goliaths and suggest that Americans give Mack's upstart a try, but Mack says he's not going after the surf-riding set, the all-night disco crowd or the "wild picnic parties."

Mack thinks his rivals' ads portraying such scenes are appealing to a fringe crowd. He says he wants the people "who are basically concerned with the cost of their grocery bills and the high cost of living." His rivals say that sales approach is out of date in an age in which one cola has claimed it has a generation and another is a natural.

Mack has had failures with colas since leaving pepsi, but he never had one that tasted as good as King and he never was able to put together the kind of distribution system he now is planning, Mack says.

His new office is full of various designs for King-Cola cans and he keeps a closet full of the cola for visitors to sample.

The only old-fashioned note is the black-and-white photograph hanging over his desk. It's of one of his friends and heroes, Calvin Coolidge.