Margaret Hamilton, the actress whose role as the cackling Wicked Witch of the West in ''The Wizard of Oz'' unnerved generations of children, died yesterday, apparently of a heart attack, at a nursing home in Salisbury, Conn. She was 82 years old.

Miss Hamilton was a gentle, lively woman who taught kindergarten for years before she began a career of 50 years in the theater, movies, radio and television. But she seared a fearsome image on the public consciousness in 1939 when, at the age of 36, she played the Wicked Witch, the terror of Judy Garland's long dream in the classic film of L. Frank Baum's story.

With a saber-like nose, arrowhead chin and a withering scowl, Miss Hamilton persuaded the young that Dorothy would never return home to Kansas by uttering lines like: ''Now you beauties. Something with poison in it. Heh! Heh! Heh!''

Her screeching laugh sent shivers up the spines of the children who filled the movie theaters and those of later generations who saw the movie replayed almost annually as a television holiday special.

''She was always afraid of the impact it had on kids,'' her son, Hamilton Meserve, the publisher of a chain of newspapers in Dutchess County, said yesterday. ''She was constantly trying to reassure children that this was make believe.''

Taught Kindergarten

Miss Hamilton was born in Cleveland in 1902, the daughter of a prominent lawyer. She wanted to be an actress, but her parents insisted she learn a profession by which she could support herself. She was teaching kindergarten at the Rye (N.Y.) Country Day School when she helped a friend audition for a part in the 1932 Broadway play ''Another Language'' and won for herself the part of Helen Hallam, a waspish wife.

A surprise hit, the play was made into a movie and became Miss Hamilton's ticket to Hollywood. In character roles in more than 70 films, she found herself playing a succession of stern spinsters, prim Yankee aunts or other unpleasant women.

She played, among other movie roles, a prudish busybody who detested Mae West in ''My Little Chickadee'' (1940); a reproving spinster in ''George White's Scandals'' (1945); a political boss's maid in Frank Capra's ''State of the Union'' (1948) and an ill-tempered dowager in ''Brewster McCloud'' (1970).

She frequently interrupted her film career to take roles in repertory and regional theater and played in the Lincoln Center productions of ''Showboat'' and ''Oklahoma.'' For 51 weeks during the mid 1970's, she played Mme. Armfeldt in the touring company of ''A Little Night Music.''

She also had running parts in such television series as ''The Egg and I'' and ''Ethel and Albert'' and two soap operas. And she was known to viewers of television commercials as Cora, the New England storekeeper who sells only Maxwell House coffee.

Miss Hamilton remained active with children, founding a kindergarten in a Beverly Hills church and serving as president of that community's board of education.

In addition to her son, she is survived by three grandchildren.

Services will be private, and a memorial service will be held later.