Four years after Westchester County entered into a landmark desegregation agreement with the federal government, relations between the two sides are hanging by a thread amid federal threats of contempt suits and revocation of money. The showdown is raising unsettling echoes of the disastrous 27-year-long court fight over housing that virtually bankrupted Yonkers, the county’s largest city.

The United States Justice Department last week sent Westchester officials a letter saying that the county had failed to enact legislation prohibiting housing discrimination based on source of income as ordered by the settlement and by a federal court ruling. The letter said the Justice Department would seek a contempt ruling against the county and County Executive Robert P. Astorino if he did not comply by Thursday.

Additionally, the federal Department of Housing and Urban Development has said it will revoke $7.4 million in money allocated to Westchester and send it elsewhere if the county does not take steps to comply with at least two elements of the settlement by the same date.

With the deadlines looming, the Westchester County Board of Legislators voted 12 to 4 on Monday to authorize a lawsuit challenging HUD’s decision to take away the $7.4 million, which would have gone to support housing and community needs.

Mr. Astorino, a Republican who was elected after the settlement was reached and has made his opposition to elements of it a centerpiece of his administration, used his annual State of the County address on Tuesday to reiterate his stark differences with the federal government.

He accused the federal government of going beyond the original agreement, trying to undermine all zoning decisions in the county and making “outrageous” demands not in the agreement.

“Washington bureaucrats, who you will never see or meet, want the power to determine who will live where and how each neighborhood will look,” he said. “What’s at stake is the fundamental right of our cities, towns and villages to plan and zone for themselves.”

He added: “Westchester residents didn’t stop becoming American citizens the day the deal was signed in 2009.”

The complaints have vividly shown the tensions between Westchester and federal housing officials since the Obama administration and the county reached one of the most ambitious desegregation settlements in decades, after a discrimination ruling against the county in 2009. In the settlement, the county agreed to create 750 houses and apartments for moderate-income people in overwhelmingly white communities and aggressively market them to nonwhites in Westchester and New York City.