Sen. Jeremiah Denton (R-Ala.) mounted an aggressive defense of his candidate for a federal judgeship in Alabama yesterday, saying liberal critics and the news media have "distorted" a string of controversial remarks attributed to Jefferson Beauregard Sessions III.

But Joseph R. Biden Jr. (Del.), ranking Democrat on the Senate Judiciary Committee, said the Reagan administration should withdraw the nomination solely because of comments that Sessions acknowledged making at a hearing last week. He called Sessions' chances of winning confirmation "bleak."

At a second hearing yesterday, supporters praised Sessions' record as U.S. attorney in Mobile while opponents accused him of racial prejudice.

Denton said Sessions had been "indicted in some newspapers" for remarks made "in off-the-cuff and private conversations." Denton also said Sen. Edward M. Kennedy (D-Mass.) had told him "he had no problem" with Sessions' unsuccessful prosecution of three black activists in Perry County, Ala., on voting fraud charges last year. The case sparked charges of selective prosecution.

But Kennedy later rebutted Denton's statement, saying, "I find the Perry County case very, very troublesome." Kennedy said he had told Denton only that he is "most concerned about the racist remarks which Mr. Sessions has acknowledged he made."

Denton emphasized that two Justice Department civil rights lawyers whose depositions were cited last week have withdrawn one allegation: that Sessions had blocked a civil rights probe by the Federal Bureau of Investigation. The lawyers apologized for faulty recollection and said they learned after checking records that the case involved Sessions' predecessor.

But Justice Department attorney J. Gerald Hebert stood by his earlier testimony that Sessions had negatively characterized the NAACP and American Civil Liberties Union. "He said he thought they were un-American" and "were trying to force civil rights down the throats of people," Hebert said in a deposition.

Denton stressed Sessions' explanation that he was not calling the groups un-American but was saying "that some people might perceive . . . that some of the things they're saying might be un-American," particularly on foreign policy.

New testimony prepared by Thomas Figures, a black who resigned as an assistant to Sessions, buttressed Hebert's account yesterday. Figures said Sessions told him "that he believed the NAACP, the Southern Christian Leadership Conference, Operation PUSH and the National Council of Churches were all un-American organizations teaching anti-American values.

"This statement clearly was not intended as a joke," Figures testified. "Mr. Sessions was extremely grave as he spoke, and he raised his voice . . . . At no time in this exchange did Mr. Sessions refer to the opinions of third parties . . . . He was without question describing his personal . . . position."

Three senior Justice Department officials testified that they respected Sessions and that he had cooperated fully in civil rights cases. One said Sessions was clearly joking when he said he had respected Ku Klux Klan members until learning that some smoked marijuana. Larry D. Thompson, a black and former U.S. attorney in Atlanta, called Sessions an "honest man untainted by racism."

Seven of eight Democrats on the 18-member panel are expected to oppose Sessions, with the stand of Howard Heflin (Ala.) unknown. Republican Sens. Charles McC. Mathias Jr. (Md.) and Arlen Specter (Pa.) are likely to oppose him, which would kill the nomination.