Atlanta officials, federal and state regulators and clean-water advocates will have their day in court Thursday as U.S. District Judge Thomas Thrash considers a request to give Atlanta 13 extra years to finish mandatory sewer upgrades.

Instead of facing a July 1, 2014 deadline, the city would have until mid-2027 to complete work under a proposed agreement.

The request is crucial to the city’s plans. Atlanta officials have promised that current water and sewer rates — already among the highest in the nation — will not rise for another four years if the extension is approved. More time, officials said, would save millions of dollars in construction expenses by freeing the city from paying top-dollar for work under a tight deadline.

Atlanta is under a federal order to upgrade its sewage system to prevent the kind of sewage spills that repeatedly fouled local waterways and neighborhoods in the 1990s.

Both the federal Environmental Protection Agency and Georgia’s Environmental Protection Division have signed off on the city’s request for more time. So has the Chattahoochee Riverkeeper, which sued Atlanta in the mid-1990s over the spills, spurring the federal government to step in.

“Given the city’s good-faith efforts to date, which have resulted in significant water quality improvements in the river and tributaries, Chattahoochee Riverkeeper supports the deadline extension and will continue to monitor the work until it is completed,” said Sally Bethea, the group’s executive director.

In announcing its support for the extension, the EPA said it wants an outcome “that is fair and reasonable to the people of Atlanta” but also protects the environment.

That leaves Thrash, who has veto power over the proposal. A court staffer said the judge declined comment Wednesday.

The city says it has spent more than $1.5 billion on required improvement projects and plans to spend another $445 million. Atlanta cut sewage overflow volume by 97 percent from 2004 to 2011.

Earlier this year, Mayor Kasim Reed said the extension would allow the city to complete vital infrastructure repairs that reduce sewage overflows and protect drinking water without putting further burdens on ratepayers.

Atlanta officials declined to comment Wednesday.