The American cartoonist and social realist painter William Grooper died Thursday of a heart ailment at North Shore University Hospital, Manhasset, N.Y. He was 79.

Mr Gropper's paintings, like his editorial cartoons, were bitten with acid of social protest. They were often compared ot the works of the art world's best known satirists such as Honore Daumier and George Grosz.

Mr. Gropper was the son of poor Jewish immigrants, born into the turn-off-the-century melting pot of the Lower East Side of New York, and he never forgot his roots. "I'm from the old school, defending the underdog," he once wrote.

In "American Art of Our Century Lloyd Goodrich wrote that Mr. Gropper was a leader of the social school, which was born of the Depression and Hitler's rise to power in Germany, and included such artists as Grosz. Ben Shahn and Philip Evergood.

"Their veteran was William Gropper," he said, "long a radical cartoonist, whose strong convictions gave edge and intensity to his drawings.

"A more sophisticated artist than most cartooists, he also presented his ideas in paintings that had the "A more sophisticated artist than most cartooists, he also presented his ideas in paintings that had the forceful imagery of his graphic work, and an added element of evocative symbolism."

Although Mr. Gropper's sympathies clearly lay with the working man and society's outcasts, his works can be found in such in congruous places as the offices of the Schenley Corp. in new York and the Department of the Interior here.

They can also be seen in the Phillips Collection and the Library of Congress here, the Metropolitan Museum of Art, the Museum of Modern Art and the Whitney Museum in New York, and in most major museums across the country.

Like most youngsters on the Lower East Side, Mr. Gropper grew up more on the street than in the home. Even before entering school he used to sketch on the sidewalks with chalk.

At the age of 12 he got a job as a dishwasher in a Bowery restaurant, and began study drawing at night. Later he worked for a clothing store, and as part of his job he had to send out postcards to the customers.

He found the job boring so to relieve the tedium he began to draw tiny figures in the corners of the postcards. Some customers asked the proprietor of the shop whether it was a new advertising gimmick. When he discovered that young Gropper was doing it, he gave his several hours off a week to continue studying art.

By 1917, at the age of 19, Mr. Gropper was so accomplished that the New York Tribune hired him as its staff cartoonist. It was while working for the Tribune that the previously apolitical artist became radicalized.

In 1918, he was assigned to go out with a reporter to cover a Justice Department raid on the headquarters of the Industrial Workers of the World, a revolutionary union organization.

Mr. Gropper returned without a story and with much sympathy for the IWW, which, he said later, hastened his departure from the Tribune.

He left the Tribune in 1919, and began supporting himself with contributions to radical publications such as Revolutionary Age, The Liberator and the New Masses.

After a stint as a merchant seaman and a construction foreman in Cuba, he returned to New York and sold cartoons and drawings to magazines such as Vogue and Vanity Fair. In 1924, he married Sophie Frankle, a bacteriologist, and began working for the Freiheit, a Yiddish Communist daily. Later he drew for the Sunday edition of the Communist Daily Worker.

He had been painting seriously for many years, but his first exhibition was at the A.C.A. Gallery in New York in 1935. That same year the produced one of his most famous works while on a Vogue assignment in Washington. The Painting, called simply "Senators," was characterized as follows by Jacob Rashell in his book, "Jewish Artists in America".

"A few deft lines and splotches of paint instantly convey the unrelieved banality of some of the distinguished representatives of the people."

Mr. Gropper's left-wing affiliations brought him to the attention of Sen. Joseph E. McCarthy's Internal Security Committee in 1953, and he was on of a number of artists who took the Fifth Amendment when called to testify.

After his appearance before the McCarthy Committee, his works were banned from State Department traveling shows and a number of museums and galleries canceled exhibitions.

For a while, as realistic art grew less and less fashionable, his work was eclipsed, but by the late 1960s, his paintings and graphics were once again receiving attention.

He painted actively until last year when he became ill.

Mr. Gropper is survived by his wife and two sons, Gene and Lee, all of Great Neck, N.Y.