The Pepsi-Cola Company next month will begin test-marketing Pepsi A.M., a cola drink with about 28 percent more caffeine an ounce than regular Pepsi but 77 percent less than coffee or tea.

The test is the most aggressive move yet by a major beverage company to encourage soft-drink consumption in the morning. Soft-drink makers have only a fraction of the market for beverages consumed in the morning, and industry analysts say recent declines in coffee consumption provide an opening for soft-drink marketers.

For the last three years, Pepsi's bigger rival, the Coca-Cola Company, has been providing its bottlers with advertising for use at their discretion that promotes ''Coca-Cola in the morning.''

Anthony Tortorici, a spokesman for Coca-Cola, said bottlers serving about 40 percent of the country were using the campaign.