Kitty Dukakis' recent episodes of heavy drinking after overcoming a long dependence on diet pills form a sadly typical pattern of switching from one abused substance to another, doctors say.

"Drug switching does occur, and the drug that's easiest to switch into is alcohol," said Dr. Roger Weiss of McLean Hospital in Belmont. "It's easy to get, cheap, legal and the most socially acceptable."Experts said that most researchers now reject the once-popular idea that some people have addictive personalities. Instead, people with addiction problems typically have little in common other than their addictions.

Weiss said that people who abuse more than one drug may be "addicted to mood change, not just to a particular drug."

On Monday, Gov. Michael S. Dukakis said that his wife had been admitted to the alcohol treatment program in Newport, R.I.

Mrs. Dukakis was treated in 1982 for a 26-year reliance on amphetamines. However, the Democratic governor said his wife had never had a drinking problem until shortly after he lost the presidential election on Nov. 8.

"Unfortunately, a combination of physical exhaustion, the stress of the campaign effort and the post-election let-down all combined to create a situation in which, on a limited number of occasions while at home, she has used alcohol in excessive quantities," he said.

Several doctors praised Mrs. Dukakis for seeking help after such a relatively brief siege of alcohol problems.

"For a public figure, who knows any revelation about problems is going to be widely publicized, it takes great courage to seek treatment," said Dr. Domenic Ciraulo of New England Medical Center.