In a partial retreat from an earlier statement that formed a cornerstone of his defense, D.C. City Council Chairman Sterling Tucker has acknowledged under oath that he never discussed the propriety of his employment at Howard University with Sen. Thomas F. Eagleton, former chairman of the Senate District Committee.

Contending that Tucker's work at the school violated the Home Rule Charter's restrictions on outside employment by the Council chairman, D.C. Corporation Counsel John R. Risher Jr. asked the Superior Court on June 6 to remove Tucker from office.

Tucker said at the time - and has publicly maintained since that his employment was not improper. "I believe it's clear," he said, that I accepted the Howard lecturing assignment only after seeking and receiving assurances from the leadership of the appropriate congressional committees, before I began the assignment, that I would not be in violation of the Home Ruled Act."

In a deposition taken July 22 as part of the case, however, Tucker conceded under questioning from Risher that he had discussed the propriety of the Howard job only with Robert Harris, who was then chief legal counsel to the Senate committee.

"I did not have direct conversation with Sen. Eagleton," Tucker said. "Robert Harris related to me the senator's position."

Tucker said in the deposition that he did discuss the legality of his work at Howard with Eagleton's counterpart, House District Committee Chairman Charles C. Diggs Jr. (D-Mich.). But Tucker received only an informal verbal assurance from Diggs that the Howard job would be proper, according to the court papers.

When he later wrote to Diggs asking for an official response, Tucker again was given a verbal assurance, but this time by Robert B. Washington Jr., who then was chief counsel to the House committee.

Risher, citing the testimony, said yesterday that Tucker's reliance on those statements "was not in good faith and was unfounded," and again asked the court to declare the Council chairman in violation of the law and oust Tucker from office.

Risher's request yesterday came in what are expected to be the final papers filed by both sides before the Oct. 19 date set by Judge Harold H. Greene to hear oral arguments in the case.

Risher in court papers filed last week, broadened the accusations by contending that Tucker's employment at Howard and his receipt of lecturing fees from a private Washington foundation also violated the city's conflict of interest codes.

Tucker's lawyers also filed legal papers yesterday and in effect, reiterated their contentions that nothing improper was done and Tucker should not be removed from the office for four major reasons.

Those reasons are that Tucker, with the assurance of congressional leaders, undertook the job in good confidence and did not try to conceal his income from it; that the employment was not prohibited by law; that Risher's contentions are meaningless because Tucker stopped lecturing at Howard on May 31; and that even if Tucker did violate the law, removal from office is too harsh a form of punishment.

Tucker's lawyers alleged that by adding the conflict-of-interest charges late in the court proceedings, Risher had attempted to commit "character assassination" of the Council chairman.

Tucker worked as a lecturer in the Howard School of Social Work from 1974 to 1976 and received $18,000 in pay, according to the court papers. His job was to teach a course in urban planning - which frequently met at his office in the District Building and attended City Council meetings - and to deliever lectures.

The other major income of Tucker's under contention is $2,250 he received in 1976 and 1977 from the Washington Workshops Foundation, a nonprofit group that runs seminars to teach youths about government. Risher contends that Tucker's work for Howard and the foundation was nothing more than "an extension of his position as chairman, pursued for profit."