Seven-Up is escalating the soft drink war, launching a new advertising campaign that points an accusing finger at the presence of coloring and food additives in Coca-Cola, Pepsi, Dr. Pepper and its other major competitors.

The advertising campaign, to be announced today, emphasizes "how clean and pure" Seven-Up looks and how "unspoiled" it tastes, while citing the artificial coloring and flavors in competing sodas.

Seven-Up's competitors already are describing the new pitch as "insidious," in keeping with the strident tone of the cola wars, which have produced a barrage of new, no-caffeine and low-calorie drinks in the past year.

Last Friday, Coca Cola U.S.A. mailed letters to an estimated 2,000 bottlers and field personnel around the country, alerting them that Seven-Up was planning a campaign that would "create negative consumer attitudes toward soft drinks containing added colors and/or flavors." That would include virtually all soft drinks outside the lemon/lime category, the letter said.

Thomas E. Dannemiller, executive vice president of Coca Cola bottler operations, signed the letter, which described the Seven-Up plan this way:

"We believe this campaign is false, misleading and detrimental to the soft drink industry because by implication the commercials say that such soft drinks have an unclean, spoiled taste. Further, it is a disservice to the American public which may become confused by the suggested messages of this insidious campaign."

Dannemiller said that Coca Cola "must vigorously insure that consumers are not misled by such disparaging innuendoes" and he promised that the company will come forward soon with "an integrated marketing plan taking full advantage of this opportunity to communicate positively and aggressively the product attributes of Sprite."

Coca-Cola officials declined comment yesterday, saying it would be "unfair" to make a public statement until after Seven-Up has formally unveiled its campaign.

Meantime, Seven-Up representatives were telephoning the media, notifying reporters of the press conference and of the Coca-Cola letter.

Mailgrams sent by Seven-Up to newspaper offices billed today's press conference as "The Soft Drink Wars, Part II." The lead sentence said:

"It was little over a year ago that the Seven-Up Company changed the face of the soft drink industry, triggering competitor's attacks that have become known as 'the soft drink wars.' " The issue that time was Seven-Up's plan to emphasize that Seven Up had no caffeine, a widely used stimulant added to most other major soft drinks.

Seven-Up "has never contained caffeine and never will," said Edward W. Frantel, president and chief executive officer of the Seven-Up Co.

The no-caffeine strategy triggered outcries from competitors but other major soft drink manufacturers followed the Seven-Up lead, either by introducing a caffeine-free product or by stopping the addition of caffeine to existing brands.

Coca Cola finally introduced decaffeinated versions of Coke, diet Coke and Tab only a few weeks ago.

That move has been accompanied by a marketing blitz, including the introduction of new products, new pricing and new distribution. One business publication, reviewing the company's behavior, said Coca Cola has "embraced a new operating philosophy: all-out attack."