Two weeks ago, customers entering a bank in Potomac were baffled to find literature promoting the Ku Klux Klan stacked beside the deposit slips.

And a Silver Spring shopper assumed the paper she found pinned beneath her windshield wiper recently was just another sales flier--until she saw it was emblazoned with a Nazi swastika and an anti-Semitic message.

Though some believe such hate literature is protected by the constitutional right of free speech, a new bill introduced in Annapolis last week by Del. Luiz Simmons (R-Montgomery) would outlaw its distribution and provide jail terms and stiff fines for people passing it out.

Simmons said the bill is designed to halt the spread of anti-Semitic and racial-hatred activities, which are on the increase across the state. "We undoubtedly will be challenged on whether this legislation infringes on First Amendment rights to free speech," he said. "But I believe that the First Amendment was never intended to protect all expressions of free speech. Obscene material is not protected, and material designed to inflict distress is not protected by the Constitution."

Some civil libertarians disagree. "We think the bill is completely contrary to First Amendment rights," said Arthur Spitzer, legal director of the Washington area American Civil Liberties Union. "It makes it a crime to say bad things about groups of people like blacks and Jews. The big problem is that there's no way to separate out the kind of comment the sponsor of the bill is upset about and the political and social debate one must tolerate in a democracy."

Spitzer said a similar law in Illinois was upheld by the U.S. Supreme Court in a 5-to-4 decision in 1952. "Most legal authorities say they don't believe the Supreme Court would come out the same way on the issue that it did 30 years ago," he said.

Del. Gerald J. Curran (D-Baltimore), vice chairman of the House Constitutional and Administrative Law Committee, said: "I feel the bill could be enacted, if we can get around the constitutional concerns."

Simmons' bill would ban any "defamatory matter" such as books, magazines, newspapers, or other printed material, photographs and recordings that "holds the citizens of any race, color, creed, or religion up to public contempt, shame, disgrace. . . "

A person convicted under the statute could face up to a year in jail and up to a $1,000 for the first offense. Subsequent convictions could result in up to three years in jail and up to a $5,000 fine.

Between July and the end of December 1981, 345 incidents of racial hatred were reported to the Maryland Commission of Human Relations through local police, said JoAnne Evans-Anderson, director of community relations for the group. Montgomery County reported 72 incidents--the highest of any county in Maryland--while Baltimore County followed with 63 reported incidents.

In recent months, Anderson said, Montgomery residents have reported literature found at school by elementary and high school students, fliers found on counters in banks and libraries and literature received through the mail or stuffed into private mailboxes at night.