NEW YORK (AP) _ Growth in the soft drink industry slowed last year but Coca-Cola's lead over second-place Pepsi widened, two closely-followed reports on the industry said Monday.

The recession and price discounting were cited for the slower overall growth rate, while Coca-Cola's gains reflected its capture of two major fast- food restaurant accounts from Pepsi in 1990.

Both reports also detected a slowdown in growth of the diet segment's share of the soft drink business.

The trade newsletter Beverage Digest said industrywide sales rose 1.8 percent to a record $47 billion at the retail level in 1991 compared with 2.8 percent growth the previous year.

A separate report from John C. Maxwell Jr., soft drink industry analyst for the investment firm Wheat First Butcher & Singer, said industry sales volume rose 1.6 percent last year compared with 3 percent in 1990.

That is the slowest growth rate since 0.5 percent in 1975, according to Maxwell's figures.

''When you have a real bad economy, people turn on the tap water. It's free,'' Maxwell said in a telephone interview from Richmond, Va.

Beverage Digest Publisher Jesse Meyers said the recession has pinched the budgets of many consumers.

He said that is evident in the increased market share for private label soft drinks, such as store brands, which are often sold at lower prices than national brands.

Meyers said private label brands captured 8 percent of the market last year, up nearly a full percentage point in three years.

Both reports said Coca-Cola's lead over Pepsi in market share increased for the year, mainly because of the Pepsi-Cola Co.'s loss of the Burger King and Wendy's fast food restaurant business to Coca-Cola Co. in 1990.

Beverage Digest said Coca-Cola Classic remained the best-selling individual brand with 20 percent of the market in 1991, unchanged from a year ago. Pepsi's share fell to 18.4 percent, down from 18.8 percent the previous year.

Maxwell's figures said Coca-Cola Classic's market share rose to 19.5 percent from 19.4 percent in 1990, while Pepsi's share fell to 16.7 percent from 17.3 percent a year earlier.

Coca-Cola Co. also widened its lead in share of the market over Pepsi-Cola Co. when all of their brands are taken into consideration, both reports said.

Beverage Digest said Coca-Cola's overall corporate share of the soft drink market rose 0.1 percentage point to a record 41.0 percent in 1991, compared to 32.8 percent for Pepsi-Cola, which fell 0.4 percentage point from 1990.

Maxwell said Coca-Cola's corporate share rose to 40.7 percent from 40.4 percent, while Pepsi-Cola fell to 31.7 percent from 31.8 percent.

Gary Gerdemann, a spokesman for Pepsi-Cola, said Pepsi's case volume grew last year and said the changes in market shares were volatile and relatively insignificant.

Both reports noted a slowdown in the growth of the diet segment's share of the market last year to about 0.3 percentage point over 1990.

Maxwell put it at 29.8 percent of the market, while Beverage Digest estimated it at 27.4 percent. Recent growth was 2 percentage points a year.

Maxwell attributed the slower growth to increased popularity of alternative beverages such as flavored waters and teas.

The fastest growing soft drink brand last year was Dr Pepper, which added 0.6 percentage point to its shares of industry sales to 5.5 percent, Beverage Digest said.

Dr Pepper came in fifth among the soft drink brands, trailing Coca-Cola Classic, Pepsi and their diet versions. Diet Coke came in third with 9.3 percent of the market in 1991 while Diet Pepsi was fourth at 6.3 percent.

Rounding out Beverage Digest's Top 10 beverage brands were Sprite and Mountain Dew, tied for sixth at 3.9 percent of the market; 7Up at 2.6 percent; Caffeine-Free Diet Coke at 2.4 percent and Caffeine-Free Diet Pepsi at 1.7 percent.