Rep. Clarence D. Long, the dean of Maryland's congressional delegation, this week delivered a speech laden with racial references that angered and offended a black audience in his home district.

Appearing before the Baltimore County chapter of the NAACP, the 71-year-old Long said that he believes blacks "are genetically superior . . . because Southern white blood flows in every black today."

The restive audience at the Woodlawn High School cafeteria began shouting at Long at that point, but the nine-term congressman continued his remarks, saying that unemployment occurs because "either you are undereducated or just don't want to work."

Long was admitted to Johns Hopkins Hospital on Thursday, the day after the speech, and has not been available for comment. His press aide, Jeff Baron, said Long went to the hospital for "an overnight checkup for a sore throat" and that he planned to return to his home in suburban Baltimore last night.

Neither Baron nor other members of Long's staff would comment on the controversial speech which was made Wednesday night.

The suggestion by Long that some blacks do not have jobs because they are lazy, prompted civil rights activist Juanita Jackson Mitchell to call out, "That's a lie that must be put to death. They want jobs, but they can't find them."

The largely black audience of 50 applauded Mrs. Mitchell when, in a voice quaking with emotion, she decried "the old shibboleth that we don't want to work."

Long answered that "I don't want to be misunderstood. I don't know the black community very well, but I do know the white community, and a lot of them don't want to work. They don't want to stay sober. They come to me pickled, people who steal . . . light-fingered . . . there's no way to wave a wand and get jobs for people who don't want to work."

James R. Pennington, the local NAACP president, answered Long by agreeing that "there are some young blacks who want to work and some young blacks who don't want to work, but there are lot more that want to work than can."

Pennington began shooting to Long that "if you are not going to do something within the next 60 days about getting jobs, we're going to forget you."

Pennington told Long that the 1980 census would show that his previously nearly all-white district was now 10 percent black.

Long's retort was, "I'll see anybody who's sober and doesn't carry a gun."

Mrs. Mitchell's husband, Clarence M. Mitchell Jr., the NAACP's long-time Washington representative, had introduced the white-haired congressman 30 minutes earlier as his "good friend" whose record during 17 years in Congress proved that he was "highly supportive of black issues and initiatives."

Other statements that caused a stir during an hour-and-a-half question-and-answer period that followed a 20-minute speech included Long's observation that blacks were strong because their ancestors had faced the rigors of Africa and survived slavery in this country.

"Physically, we [whites] wouldn't be able to win all those trophies in the Olympics" as blacks do, Long said.

Long said the absence of blacks on his congressional staff resulted from blacks making such "tremendous gains" in employment opportunities that "the first-rate blacks don't want to work for me."

He added that he did not want to hire someone who would be surrounded by "brighter" people. "I would be accused of hiring one just because he's black. I have to have topflight white people I have to have top-flight colored people."

Long, widely called "Doc" by his Capitol Hill colleagues because he was a professor of economics at Hopkins for 18 years before his election to Congress in 1962, urged blacks to get more education as a way of improving job opportunities.

He told a story about a black woman who failed to get a job because she misspelled the first word on her resume, to which a woman in the audience answered, "whites misspell words too, but they get hired."

Noting the mounting hostility of the audience, Long said, "I better watch what I say around here, my God." Referring to himself, he added, "Let's face it, a lot of us have blinders on. There's bound to be things I don't know about."

Before Long checked into the hospital Thursday, he telephoned Pennington, an official with HEW in Washington, and castigated him for being "obnoxious, offensive and critical" of his staff and told the NAACP leader not to call his congressional office any more, Pennington said.

"He lost his temper," Pennington said. "He's famous for his temper tantrums."

Pennington said yesterday he still is "anxious to work" with Long, and that the exchange had "no political implications. It's not my desire to embarrass him anymore than he's embarrassed himself. I plan to work with him toward solving the critical unemployment problems we face."

But Long's opponent in the May 13 Democratic primary, State Del. Thomas B. Kernan, 31, yesterday said "we need some new ideas. It is unfortunate in 1980 that we still hear that kind of rhetoric."