DALLAS, DEC. 9 -- The narrow defeat of a referendum designed to help minorities win City Council seats could throw the issue back to a federal judge who has vowed to impose either the same plan or a similar one, officials said today.

Voters on Saturday rejected by just 369 votes a referendum that would have created a system to elect 14 council members by individual districts and elect the mayor at large.

Opponents said the system would have resegregated Dallas. They backed a plan voters approved in August 1989, calling for 10 candidates to be elected by district and four by region and for the mayor to be elected by voters citywide. That earlier proposal never was implemented because a federal judge suggested he would rule it unconstitutional.

The referendum was held as part of the settlement of a 1988 federal lawsuit brought by Roy Williams and Marvin Crenshaw, who failed in their at-large council bids. The men, both black, charged that the existing election system made it

difficult for minorities to win election.

Black and Hispanic leaders nationwide have long charged that at-large elections dilute minority candidates' political power and make it difficult for them to win office.

Under the current system, instituted in 1975, eight council members are elected by voters in individual districts and another three, including the mayor, are elected by voters citywide.

Proponents of the plan that was rejected Saturday said they would seek a recount because of the slim margin.