When Warren Richardson, the former general counsel of Liberty Lobby, asked that his impending nomination as assistant secretary of health and human services be dropped because of allegations of anti-Semitism, he spared the Reagan administration as unpleasant and potentially damaging fight.

Richardson, in a letter to HHS Secretary Richard S. Schweiker late Friday night, denied he was anti-Semetic, but declared that "political realism" was forcing him to withdraw his name.

Schweiker accepted Richardson's withdrawl "with regret" and said that "after careful review," there was "no convincing evidence" that Richardson was anti-Jewish or racist. Department sources said Richardson, who had been serving as Schweiker's special assistant while waiting for his nomination to be sent to Capitol Hill, will withdraw from that post as well.

Had the Reagan camp persisted in the nomination, it faced a serious fight in which the administration and conservatives, rightly or wrongly, would have appeared to be defending bigotry and anti-Semitisn. That is a liability they didn't need, especially when the administration is already in conflict with Jewish groups over the sale of AWACS radar surveilliance planes to Saudi Arabia.

Attempts were under way, apparently with prospects of success, to enlist the Leadership Conference on Civil Rights, a huge group of black, labor, religious and welfare organizations, in fighting the Richardson nomination.

Sen. Edward M. Kennedy (D-Mass.), who worked closely with Schweiker on health matters during Schweiker's Senate days, was preparing to denounce the nomination in a speech tonight in Massachusetts and lead a fight against it in the Senate. He had withheld public fire earlier in hopes Schweiker would drop the nomination.

Richardson had become friendly with many senators -- including Schweiker, though the then-senator was on the opposite side -- during the fight over a labor law reform bill three years ago when Richardson led a coalition of business and conservative lobbyists opposing the bill.

However, it was Sen. Paul Laxalt (R-Nev.) who pushed Richardson for a government post, proposing that he become White House chief of lobbying. Aides said Laxalt didn't know that Richardson had ever been with Liberty Lobby.

When Richardson didn't get that job, his name popped up for chief Hill lobbyist for HHS. Schweiker and his top aide, David Newhall, who both knew and liked Richardson, approved the idea.

Richardson did put on his resume that he had worked for Libery Lobby, but Newhall, according to one source, thought that was a reference to the so-called "liberty amendment" to repeal the income tax.

Richardson, who also worked at various times for the National Right to Work Committee, National Lumber Manufacturers Association and Associated General Contractors, served as general counsel of Liberty Lobby from 1969 to 1973.

During that period, publications or officals of the organization charged, among other things, that Jewish bankers were financing world communism, that Zionism was a plan to take control of the world and that school desegregation was a plot to melt all races into one "U.N. brown man."

A 1971 article in The New York Times, bearing Richardson's byline, opposed any U.S. intervention in the Mideast and said, "Liberty Lobby will not tag along with the cowards who would rather countenance another national disaster than brave the screams of the pro-Zionist 'free press' in America."

Last week, Rep. Sam Gejdenson (D-Conn.), the Anti-Defamation League of B'nai and the American Jewish Committee charged that Liberty Lobby was an anti-Semitic and anti-black organiztion and that Richardson's association with it should disqualify him from the HHS post.

Richardson denied he held those views and, in a memo to Newhall, said, "I condemn unequivocally the anti-Jewish and racist actions of the Liberty Lobby." He said he had not written any of the Liberty Lobby material cited and that someone else had inserted the offending sentence into The New York Times article.

He further said he worked for the Liberty Lobby only because he needed the well-paying job.

Richardson's withdrawal has not completely quieted the uproar his nomination caused, however. Nathan Perlmutter, national director of the Anti-Defamation League, said yesterday, after Richardson had stepped aside, that there is something amiss in a system that permitted his nomination. a

"Government should not be a reservoir in which our chiefs are bigots," Perlmutter said, adding that he was concerned with selection procedures for officials that appeared to be either "insensitive to the meaning of anti-Semitism or racism or slipshod."