Rockville City Manager Richard Robinson was fired from his $70,000-a-year post last night by the City Council, fulfilling a campaign pledge by newly elected Mayor Douglas Duncan.

Robinson's dismissal is effective immediately. Duncan said the move will cost taxpayers about $35,000 because Robinson's contract, which would expire Feb. 15, insures him six months pay upon dismissal.

The action came only hours after Duncan and the council, with two new members elected Nov. 3, were sworn in to office. Stephen Abrams, who is the only member who didn't run on Duncan's slate, was the only one of the five council members to vote against the firing, criticizing the way the decision was reached.

Robinson stood outside the council chamber as his firing was announced and said later, "I'm relieved, I think . . . . But I'm partially in shock." Robinson's performance had been a key issue in this year's long election campaign, although his technical competence in the job was not questioned.

Robinson first created controversy for trying to place under his control the city attorney and city clerk, the only two positions traditionally independent of the city manager.

Later, Robinson was criticized for his relations with minorities on the city staff following the resignations of two high-ranking black Rockville officials and the departure of a third after his job was cut in a reclassification of city jobs. Those employes ultimately filed complaints with the city and state human rights commissions and one has filed suit.

After the meeting, Duncan, who defeated Mayor Steven Van Grack in the election, said, "I was pleased. It was very important for us to move very quickly on this."

Rockville Planning Director Rick W. Kuckkahn was named acting city manager.