A tentative agreement on a new three-year contract was reached last night to end an 11-day walkout by 9,000 Detroit municipal workers that threatened to disrupt the Republican National Convention, which opens Monday.

"If all goes well, workers will be back on the job by Saturday," said Lloyd Simpson, chief negotiator for Council 25 of the American Federation of State, County and Municipal Employes.

The walkout, which began at one minute before midnight June 30, had idled garbage collection and bus service. The settlement came at 11:05 p.m.

AFSCME workers are expected to hold a ratification vote at 8 a.m. today, Simpson said.

Mark Ulicny, the city's chief negotiator, said the city cannot afford the contract settlement, and raised the possibility of worker layoffs. However, he said the agreement was within a settlement framework approved by Mayor Coleman Young earlier in the week.

Bargainers said final details of the pact would not be revealed until the contract is completely ironed out.Negotiators remained huddled over the negotiating table after the tentative agreement was announced in an attempt to resolve those remaining issues.

However, AFSCME spokesman Reginald McGhee said the settlement was "probably close" to a 6 percent annual wage increase for the three years. He also said the package features a dental plan and a supplemental unemployment benefit plan borrowed from the automobile industry.