The Montgomery County Council yesterday confirmed the firing of Bert Cumby, the chairman of the Washington Suburban Sanitary Commission who had foughts for months to save his job.

County Executive Charles W. Gilchrist's choice to succeed Cumby was immediately sworn in, and the embattled ex-commissioner filed suit in Montgomery Circuit Court in an attempt to reverse the council's action.

The 4-to-2 vote against the 66 year old retired Foreign Service officer marked the first time a commissioner has been fired in the unit's 61-year history.

Gilchrist asked for Cumby's job, saying he couldn't communicate with him. Cumby was one of three Montgomery County appointees on the bi-county commission that plays a key role in controlling growth in the Maryland suburbs by allocating available sewer capacity.

His removal culminates a running political controversy in which some council members have criticized the county executive's decision as unkind and unfair. Others said the firing was necessary to assure the county proper representation on the commission.

The commission's Montgomery County members frequently feud with their Prince George's County counterparts.

The Prince George's representatives elected Cumby chairman last month, after Gilchrist announced his intention to remove him.

At yesterday's session, Council President Neal Potter said Cumby had voted contrary to the county governmentS instructions. Cumby has denied the charge. Potter, also said Cumby had "considerable problems in cooperating with the other commissioners and the executive."

Council member Scott Fosler called Cumby "a marvelous person" but said Gilchrist should have a commissioner with whom he is comfortable.

Veteran council member Esther Gelman, who abstained during the vote, called yesterday "the most shameful morning I have ever spent in these chambers." She said the removal had been "handled without grace or compassion."

The council approved Sally P. Kanchuger to replace Cumby. David R. Scotton was reappointed, and Jessie L. Maury was confirmed as a new member.

Cumby insisted that he has always been loyal to the county's interests and that Gilchrist has no right to fire him without cause.

The law setting up the sewer commission, however, entitles a member to a hearing but doesn't specifically establish grounds for removal.

Prompted by the Cumby case, State Del. Contance A. Morella (R-Montgomery) has introduced a bill in the House to require "adequate cause" for dismissal of a WSSC commissioner.