Drinking causes trouble in one out of three families in America, and that figure has doubled in six years, according to a new Gallup Poll on alcoholism released yesterday.

About 81 percent of those surveyed believe that alcoholism is a major national problem, according to the poll. That opinion also has increased. Only about 60 percent of Americans thought drinking was a major national problem in previous polls.

"It is an overwhelming figure," said George Gallup, commenting on the number at a news conference. He said it is extremely rare to find Americans in such complete agreement on any question.

Gallup said that the new poll figures probably reflect a real increase in alcoholism as well as some increase in awareness of the problem, perhaps half and half. Other indicators such as the increase in alcohol-related traffic accidents also indicate a real increase in alcoholism.

Daphne Prior, a spokesman for The National Council on Alcoholism, said that while solid figures are lacking, there has been a definite increase in the number of cases of alcoholism being reported. She said the council is unsure whether this reflects a real increase in alcoholism itself.

The Gallup poll was conducted in cooperation with the CareUnit Program, a subsidiary of the Comprehensive Care Corp., a medical conglomerate that owns the largest chain of hospital-centered alcohol-care units in the country. David Langness, a spokesman for CareUnit and the pollster at the news conference, said that the poll surveyed 1,566 adults over the age of 18 by phone.

The key question was: "Has drinking ever been a cause of trouble in your family?"

This year 33 percent answered yes. Last year, 22 percent answered yes to a nearly identical question, with only the word "liquor" in place of the word "drinking" now used. In 1976, about 17 percent answered yes, and in 1947, about 12 percent said liquor had caused trouble in the family.