An unlikely coalition of liberals and conservatives here is fighting a proposed change, backed by the city's traditional power brokers, in the way Houstonians elect their city council.

A very light voter turnout is expected in a referendum Saturday that could determine not only the city council's makeup but also whether the Justice Department will permit municipal elections in the nation's fifth largest city any time soon.

On the ballot is a proposal to enlarge the city council from eight to 14 members, with nine of the members to be elected by district and five to be elected at-large.

Currently, the entire city council is selected at-large, which the Justice Department has said violates the 1965 Voting Rights Act by diluting minority voting strength in the city.

As evidence of this, the department notes that since the current city council system was set up in 1955, only one black and no Mexican-American council members have been elected in a city roughly 25 percent black and 13.5 percent Mexican American.

In June, the Justice Department ruled that the city had broken the law by annexing largely white, suburban areas without guaranteeing minority representation on the city council through some system of single-member districts.

The ruling, in effect, suspends municipal elections here until a single-member district plan satisfactory to the Justice Department is devised. Regular city elections would normally be held on Nov. 6.

The "9-5" plan on Saturday's ballot is backed by the mayor, city council, the Chamber of Commerce and other local business groups.

Chamber of Commerce President Louie Welch, a former five-term Houston mayor, argues that a defeat for the 9-5 plan would postpone a $400 million bond election designed to refill the city's nearly depleted capital improvements fund.

Welch, who only reluctantly favors the 9-5 plan, would prefer to see the Voting Rights Act amended to remove Texas from its provisions. He says that a council with more than 14 m4mbers - as proposed by other Houstonians - would be faction-prone, unwieldy and expensive.

Most opponents of the 9-5 plan, favor such a proposal, not on the ballot, calling for 16 single-member districts and four at-large council positions.

They hope that by defeating the plan, they can later bring this 16-4 plan to a vote. Minority, liberal, labor and homosexual groups are the heart of the anti-9-5 effort.

They have been joined, however, by civic activists in the usually conservative, newly annexed white suburbs, who contend their neighborhoods would be better represented under the 16-4 plan.

The city affairs committee of the local Republican party also voted two weeks ago to oppose the 9-5 plan.