Alcoholism may well be the No. 3 killer in the United States but "you can't prove it by medical statistics" because it is so often reported as something else, according to an Arlington County alcoholism counselor.

This is a view widely held among professional workers in the field, Garth B. Oswald, of the county Department of Human Resources, told members of the Arlington Steering Committee for Services to Older Persons last week. He spoke on "Problems of Alcohol Among the Elderly" at a meeting held at the Red Cross Chapter House, 4333 Arlington Road.

Studies by federal agencies, he said, suggest that "honest" data would show that 30 percent or more of persons age 65 and over who are in hospitals are there for reasons related to alcohol.

Oswald said doctors, "being human beings," often describe alcoholic problems by other language. They do so sometimes in deference to patients or their families and sometimes because [WORD ILLEGIBLE] on treatment for alcoholism written into medical insurance contracts, he said.

He cited a hypothetical case of a woman who withdraws to herself, turns to drinking sherry wine and, 10 years later, dies as a result of it. The cause of death entered on her death certificate, he said, might be "congestive heart failure" or "pneumonia."

Oswald distributed a fact sheet entitled "Alcohol and the Elderly," written by the National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health. The paper, which buttressed his thesis that alcoholism is often diagnosed as something else, stated, "What is perceived as frailty, senility, or simply the unsteadiness of old age may in fact be alcoholism."

The fact sheet reported that people age 65 and over made up less than 5 percent of the U.S. population in 1920, but by 1976 constituted more than 10 percent. "Of the approximately 22 million Americans over 65, as many as 1.6 million may be alcoholic," it said.

Public health statistics show that heart disease and cancer are, respectively, the No. 1 and No. 2 causes of death in the United States.

Alcoholism, Oswald said, is a disease that is "a biological, sociological and psychological problem," and therefore cannot be cured simply by seven days or so of detoxification in a hospital.

Whether people disengage from society because of drink, or drink because of disengaging from society, he commented, is like the argument over whether the chicken or the egg came first.

Arlington County's 17 counselors on alcohol and drugs, he said, deal with about 400 people at any given time. Statistics are not meaningful because a problem drinker does not become part of them unless and until he or she seeks helP, he said.

More than 70 percent of people who contact the counselors, he said, do so as a result of court action, such as that set off by drunken driving. The remainder come of their own volition or under pressure from spouses, he said.

He called the fellowship program of Alcoholics Anonymous "a most wonderful program and a successful one."

Oswald was introduced by Warren Clardy, chairman of the steering committee. Its members represent a wide range of organizations, both governmental and nongovernmental, that serve senior citizens.