At PortMiami, federal dollars fund Customs agents, security operations and cargo inspectors. But with a historic cut in federal spending set to begin Friday, port director Bill Johnson must contemplate how to keep the place running with less help from Washington.

“I don’t want to have a bunch of rotten tomatoes,”Johnson said Tuesday. “Or disgruntled cruise passengers.”

This week brought similar discouraging thoughts, scenarios and forecasts from hundreds of agencies, charities and businesses throughout South Florida as the mystery of a federal spending “sequester” approached. On Friday, federal law requires the White House to begin to cut spending by $85 billion this year, the trigger from a 2011 deficit-reduction rule designed to force a compromise on bringing down the nation’s debt.

Republicans and Democrats haven’t reached a deal, and Washington watchers don’t expect one by Friday. What once seemed a remote possibility now threatens to rattle how South Florida spends at least some of its federal dollars, while leaving many to plan for contingencies they’re not sure will actually happen.

The full scope of the furlough’s impact remains unclear — both nationally and in South Florida. But as the deadline approaches, more details on cutbacks and preparations are surfacing. Here’s a look at some of the sequester’s potential impacts across the region.

EDUCATION: In Miami-Dade, where the federal government invests about $218 million a year in K-12 education, the nation’s fourth-largest school district is bracing for close to $20 million in cuts.

Superintendent Alberto Carvalho said the 9 percent sequestration rate anticipated this year by the Obama administration would strip $10.3 million from Title I funding, which provides support for academic programs for economically disadvantaged students. Another $1.7 million would be cut from Title II funding for professional development and class size reduction. And about $900,000 would come from federal funds that go toward educating English language learners — a key population in a county where close to 70,000 students were born in another country.

“We’re talking about poor children, students with disabilities and English language learners,” he said. “Some of the most fragile communities of students would be the most impacted. It’s unacceptable to us, so we budgeted in a way to protect” them.

Carvalho said that following last year’s budget stand-off and the ensuing credit downgrade by S&P, Miami-Dade schools anticipated that Congress would be unable to find a compromise to avoid the cuts come 2013. So the district spent judiciously on supply and equipment dollars, where it had discretion, to avoid trying to pull back dollars already spent, he said.

“That to us was a real strong signal and we prepared for it,” he said.

Still, Carvalho said the district is only prepared to avoid “catastrophic” programming and personnel cuts for the remainder of the year. He said another year of reduced funding would likely mean up to 350 layoffs as well as programming cuts.

AIR TRAVEL: Republicans have accused the White House of predicting severe consequences from cuts that amount to just 2 percent of the $3.8 trillion federal budget. And in the list of sequester impacts, chaos at the nation’s airports has gotten significant attention.