Baltimore City Council President Walter S. Orlinsky, at a brief but emotional session of the council, announced tonight he will plead guilty to a federal extortion charge and resign from the council.

The 43-year-old, mustachioed Orlinsky made his announcement to a hushed crowd in the high, yellow-domed council chambers, then ordered the meeting adjourned.

He quickly left the chambers, smiling wanly and shaking the hands of several well-wishers before disappearing into his private office.

Orlinsky, council president for 11 years and a durable fixture in Baltimore politics, is scheduled to plead guilty Tuesday in U.S. court here.

A 12-count indictment returned in April accused Orlinsky of accepting more than $11,000 in kickbacks from Modern-Earthline Companies of Philadelphia in return for using his official influence to help the firm obtain a sludge hauling contract from the city. Orlinsky said today that he will plead guilty to one count of extortion in connection with receiving $2,532 in kickbacks.

"I was wrong in agreeing with poet T. S. Eliot when I said April is the cruelest month," Orlinsky said in his brief statement to the Council today. "Perhaps September is."

He said, "There are seasons under the sun, and this is my season to begin ending one period of my life and to begin a new one."

Later, he said, "I expect to remain as your president until sometime prior to sentencing, as provided under the law of the state of Maryland and to assist in the orderly transfer of authority.

"At the time of my resignation, I should like to talk with you at greater length. Suffice it to say that I am deeply grateful to those of you who have been so kind and supportive during this most difficult period of my life," Orlinsky said.

Orlinsky will be sentenced by U.S. District Court Judge Norman P. Ramsey. Sentencing in federal court here customarily follows within a few weeks of a defendant's conviction or guilty plea. Federal prosecutors and Orlinsky's defense attorneys refused to discuss the terms of any plea bargaining that preceded Orlinsky's decision.

Orlinsky's announcement before the council came as no surprise since reports of his decision to plead guilty had been circulating for sevearl days. The announcement nevertheless transfixed large crowds gathered in the chambers and appeared to leave many city hall veterans stunned.

A spirited fight is expected among contenders to succeed Orlinsky on the council.

Under city procedure, Council Vice President Clarence H. (Du) Burns will act as temporary president until the 18-member council elects a permanent president, either from among themselves or from outside city hall.

The new president then will serve until the next regular citywide election.

Burns, who is thought to be favored by Mayor William Donald Schaefer, may lobby for the presidency. If he prevails, he would become Baltimore's first black council president.

Speculation on other possible contenders ranges from several sitting council members to State Sen. Harry McGuirk, recently defeated in his bid to become the Democratic primary nominee for Maryland governor.