Jefferson B. Sessions III, President Reagan's nominee for a federal judgeship in Alabama, has called the NAACP and the American Civil Liberties Union "un-American" and "communist-inspired" groups that "force civil rights down the throats of people," according to sworn statements disclosed yesterday.

Sessions, 38, the U.S. attorney in Mobile, also referred to the National Council of Churches, the Southern Christian Leadership Conference and Operation PUSH as "un-American," according to depositions by four Justice Department attorneys that were given under oath Wednesday to the Democratic staff of the Senate Judiciary Committee for Sessions' confirmation hearing.

In another controversial remark, about Ku Klux Klan members, Sessions said, "I used to think they're okay," until learning that some were "pot smokers," according to the sworn statements by the civil rights attorneys, who had worked with Sessions.

The disclosures appeared to virtually doom Sessions' chances of confirmation, according to committee sources, who said he would come under pressure to withdraw.

Sessions was already the most controversial of Reagan's judicial nominees -- and to many Democrats is a symbol of insensitivity on civil rights -- because he unsuccessfully prosecuted Albert Turner, a former aide to the Rev. Martin Luther King Jr., and two codefendants last year. The case was one in a series of voting fraud prosecutions that the Justice Department brought against black civil rights activists in rural Alabama, most of which did not result in convictions.

Sessions acknowledged making most of the comments disclosed yesterday, but said he was joking or had been misinterpreted. He said he greatly respects the National Association for the Advancement of Colored People and views the Klan as "a force for hatred and bigotry."

But he said the NACCP, the National Council of Churches and other groups are "considered un-American . . . when they involve themselves in promoting un-American positions" in foreign policy. Pressed for specifics, he cited only "the Sanctuary movement [which harbors refugees] and the Sandinistas."

Sessions also said he thinks the NAACP and the American Civil Liberties Union sometimes "do more harm than good" by "demanding things that are not justified."

Sen. Edward M. Kennedy (Mass.), leading a Democratic assault on Sessions, called him "a throwback to a disgraceful era" and said his nomination is "a disgrace to the Justice Department."

"That is the most painful thing I have ever heard . . . . It breaks my heart to hear that said," Sessions replied.

J. Gerald Hebert, a Justice Department lawyer here who submitted one of the depositions, told the panel, "I really don't know" whether Sessions is a racist. "He has made some comments that show racial insensitivity," Hebert said.

Repeatedly questioned about his statements as recounted in the sworn depositions, Sessions denied that he had called a black official in Mobile a "nigger." But he acknowledged that he had agreed with another person's statement that a prominent white civil rights attorney was "a disgrace to his race."

"I don't know why I would have said that," Sessions said. "I certainly don't believe that." He also said he did not remember calling the NAACP "a pinko organization" that "hates white people," as one of the sworn statements said, but added that he had criticized the group for taking positions viewed as "un-American."

"I'm loose with my tongue on occasion," Sessions said. "I may have said something similar to that."

Sessions called his remark about having previously respected the Klan "a silly comment" that he made to a black assistant during an investigation into the murder of a black Alabama man.

"Don't you think it was insensitive to say that in front of a black man, after a black man had just been brutally beaten and hung?" Sen. Howard M. Metzenbaum (D-Ohio) asked. Sessions said the comment was so "ludicrous" that no one could have taken it seriously.

Metzenbaum, noting that Sessions has not hired a black lawyer in more than four years in office, asked: "Could any black person come into your court and feel they had a chance of getting justice before you?"

Sessions also confirmed that he believes "that the Voting Rights Act is an intrusive piece of legislation" but added that he thinks the law has been "effective."

Democrats have sharply criticized Sessions for initiating a voting fraud probe in Perry County, Ala., which focused on absentee ballots that Turner and others gathered from elderly voters in 1984. The Federal Bureau of Investigation interviewed dozens of people whose ballots appeared altered, and elderly voters were bused 200 miles to testify before a grand jury in Mobile.

Civil rights lawyers charge that the FBI intimidated some of the witnesses. Turner said he urged elderly voters to change their ballots and made some changes himself, but that he did so with their permission.

While committee chairman Strom Thurmond (R-S.C.) held a blown-up copy of an absentee ballot, Sessions cited testimony from black voters who said their ballots had been picked up by Turner and changed without their knowledge.

"Are these the defendants that were found not guilty?" Kennedy interrupted.

"Please evaluate me on whether the indictment should [have been] brought," Sessions replied. "Cases do fail and you do lose cases."