Clarence Mitchell witnessed his first lynching 45 years ago in Princess Anne, Md., as a young reporter for the Baltimore Afro-American.

At the time, Mitchell, one of seven children in a poor black family from Baltimore, was already something of a civil rights activist, but as he watched the mob cut down the body and burn it with gasoline, his convictions deepened and helped lead to a lifelong career working for civil rights.

Now 67, Mitchell is rounding out nearly three decades as director of the NAACP Washington bureau and the nations chief lobbyist on Capitol Hill for civil rights. He will step down from the NAACP post in December, although he will remain for two more years as chairman of the Leadership Conference on Civil Rights, which he helped found in 1950.

Ringed by pictures of black leaders, presidents, House speakers and Senators, Mitchell sat in his office recently and recalled some of the people with whom he had clashed or cooperated.

Mitchell unhesitatingly singled out the late Sen. Richard B. Russell (D-Ga.) as his ablest and most effective opponent.

Mitchell said Russell was "a master tactitian, an able speaker, a great organizer." He said Russell repeatedly thwarted early efforts of civil rights forces.

"He was the de facto leader of the Senate," Mitchell said. "He could convert our potential supporters into opponetns," said Mitchell, recalling one key vote in which Russell, through a combination of flattery and persuasion, stole away the support of Sen. Eugene Milliken (R-Colo.).

But, Mitchell said, Russell was normally courteous to him.

Sen. John C. Stennis (D-Miss.) also opposed civil rights legislation but like Russell, he too was "always a gentleman," Mitchell said. "There was a complicated case where he showed real humanity - helping a black soldier involved in a traffic accident in Mississippi get back to his post in Ohio."

While many southerners were normally polite even while fighting everything that Mitchell was trying to do, other southerners could be discourteous.

"Some people were rude - [Sen. John L.] McClellan [D-Ark.], the fellow from Louisiana, Allen Ellender, and of course [James] Eastland [D-Miss.]. But Eastland's was a moderate type of rudeness."

One tactic occasionally practiced by some of these southerners was to keep Mitchell waiting for hours to testify. Once when Mitchell mildly objected that he had been waiting for about four hours while late-arriving witnesses were slipped in ahead of him, he was told that the others had important business.

During hearings in the late 1950s probing NAACP charges of racial violence in the South, McClellan and Olin Johnston (D-S.C.), standing in the hall as Mitchell walked by, pointedly raised their voices and declared, "Yts, we're going to get some of these 'boys' for perjury, talking about finding bodies in rivers."

Mitchell said that while Eastland wasn't always unpleasant "he had great trouble referring to me as mister. In [one] hearing, he knew I was scheduled to testify but instead of just calling 'Mr. Mitchell,' he just said 'Anybody else?' even though he knew I was there and waiting to testify. Before McClellan and Ellender left, they changed, Eastland [has changed] too. At least the visible attitude has changed a lot."

Mitchell said he found former Senate majority leader Mike Mansfield (D-Mont.), a civil rights backer, brusque and difficult to approach, largely, Mitchell believes, because of Mansfield's in-drawn personality rather than because he wasn't sympathetic to the cause. Mitchell said Mansfield setmed to regard lobbyists as "interlopers. When I tried to thank him for something once he almost brushed me off."

Mitchell said his fear that he wouldn't have good access to Mansfield during the struggle over the 1964 Civil Rights Act led him to urge President Johnson to make sure that Sen. Hubert H. Humphrey (D-Minn.) had a major role on the bill.

Pointing to a picture of himself and Washington attorney Joseph L. Rauh Jr., a cofounder of the Leadership Conference, at a White House meeting with Johnson, Mitchell talked about the former president.

When Johnson became Senate Democratic leader in the 1950s, Mitchell said, he called in Mitchell and said as far as he was concerned, he was for civil rights "but I don't want to break up the Democratic Party."

Johnson said he would support "executive and court action but I won't support legislation because it will break up the party." Mitchell said once Johnson saw that you could get things achieved in Congress and keep the party intact, "he started to move" and eventually became a major supporter of civil rights, particularly as president.

Mitchell said he has been disappointed with some civil rights backers in Congress who deserted the NAACP on busing. "Rep. Charles Vanik (D-Ohio) is on our board in Cleveland but left us on transportation. Jim O'Hara [formerly a Michigan congressman], one of our strongest supporters, actively worked against us on pupil transportation."

Mitchell said recently he has been extremely vexed with Sen. Abraham A. Ribicoff (D-Conn), whom he never considered a "tower of strength on civil rights." Still, "I never expected his opposition" to centralizing all government anti-job-discrimination enforcement in one agency.

Although Mitchell was quite willing to call Sen. Russell his No. 1 opponent, he refused to name his favorite civil rights supporter in Congress - although at times he seemed on the verge of saying "Phil Hart," the late Democratic senator from Michigan.

Mitchell is a big, sofe-spoken man who dislikes criticizing people even when opposing them on an issue. He even has a good word for Senate Majority Leader Robert C. Byrd (D.W.Va.), who has opposed busing and many other policies the NAACP favors: "He's very able.In his early days around here he had a black secretary in the House when nobody else did. He has an overriding ability to work hard . . . He's called back immediately" whenever Mitchell had to reach him urgently.

In the late 1940s, when he was NAACP labor secretary but already a well-known national figure through his wartime fair-employment work and postwar lobbying, Mitchell was turned away from the Senate dining room because he was black.

"They never had separate bathrooms but at the dining rooms they stopped you." This "faded out" in the 1950s. In the late 1940s blacks also were subject to discrimination in labor unions, legal segregation in schools and places of public accommodation, denied the vote in much of the South, but this too is now illegal and "fading out" - in significant measure because of the work Mitchell and his colleagues have done on Capitol Hill.