With Congress unable to reach a spending deal before its midnight deadline, many U.S. government operations screeched to a halt Tuesday, leaving Mainers who rely on federal aid for housing, food and heating oil in a state of uncertainty.

The Democrat-led U.S. Senate refused to pass a federal budget or continuing resolution that would alter President Barack Obama’s signature health care reform law — the Affordable Care Act, also commonly called Obamacare — while their counterparts in the Republican-controlled House pushed for spending plans that would cut funding for the law or delay its implementation.

“It is outrageous that the Republican obsession with weakening the Affordable Care Act has now led to a government shutdown,” said U.S. Rep. Chellie Pingree, D-Maine, in a statement. “I’m hopeful that a compromise can be reached quickly, but for now an extreme group of tea party Republicans has made good on their pledge to shut down the government in an attempt to undermine the health care reform law. The law has already benefitted millions of Americans and will allow uninsured Americans to sign up for health insurance starting today, yet these extremists in Congress just won’t let up in their crusade to repeal, delay and undermine the law.”

It represents the 17th federal government shutdown since 1976, with the longest — and most recent — of those coming during a 21-day political standoff in 1995.

With the government shutdown Tuesday, Acadia National Park joined National Park Service destinations across the country in closing down.

Federal departments each filed contingency plans in advance of the shutdown to outline how they would respond if it came to fruition. More than 800,000 federal workers were expected to be furloughed and only programs and employees deemed essential to the protection of people and property were considered exempt from the shutdown.

Mail carriers, active duty military personnel and air traffic controllers were expected to stay on the job Tuesday, as were those responsible for supporting school lunch, Social Security, Medicare and Supplemental Nutrition Assistance Program — SNAP, formerly known as food stamps — payments, which would all reportedly continue to be made.

But the U.S. Department of Agriculture announced that new federal money would not be available to support the Special Supplemental Nutrition Program for Women, Infants and Children, or WIC. On her website, Pingree said WIC payments would continue to be made through October, however.

WIC provides assistance to low-income mothers and children determined to be at “nutrition risk.” In Maine, about 26,000 people benefit from the WIC program each year, receiving nearly $13 million in annual food aid.

If Congress doesn’t reach a compromise to fund the government by Oct. 15, federal courts in Bangor and Portland will cut back operations, likely limiting the processing of civil actions and employee hours, U.S. District Court Judge John Woodcock told the Bangor Daily News on Monday.

By November, the Maine State Housing Authority will need confirmation of its allocation of federal Low Income Home Energy Assistance — or LIHEAP — funds in order to begin cutting checks to heating oil providers for the cold weather season.

MaineHousing spokeswoman Deborah Turcotte told the BDN that MaineHousing received just less than $35 million in LIHEAP funds for the fiscal year ending Monday and distributed money to approximately 55,000 qualifying Maine households.

She said the fiscal year for low-income Section 8 housing vouchers lasts until Dec. 31, so funding should be available to cover that program for another three months, but if the congressional deadlock continues into 2014, those payments could be cut off as well.

Although active duty military personnel will remain on the job, the shutdown will affect hundreds of Maine National Guard employees, Maj. Michael Steinbuchel, spokesman for both the Maine Air National Guard and Maine Army National Guard, said Tuesday.

“We have identified 280 technicians, military technicians, who will be affected by the furlough,” Steinbuchel said.

The employees are at work today while Guard leaders await official word to send them home, which may happen Tuesday afternoon, he said.

“At this point, we are waiting further guidance on the implications of that emergency furlough,” Steinbuchel said. “These employees, who provide services at the Maine Guard and maintenance facilities — they work in every department from our human resources, to logistics to maintenance.”

Once the emergency furlough order is given, the military technicians will be given a minimum of four hours to pack up belongings and depart, Steinbuchel said, adding each department has individual and detailed shutdown plans to follow.

“This does not affect those Maine National Guard employees who are deployed,” he said. “The 133rd — they’ll continue to get paid as will those [101st Air Refueling Wing] airmen deployed.”

There are 178 members of the Maine Army National Guard’s 133rd Engineer Battalion currently deployed in Afghanistan.

“Those employees that provide essential life services and security to our people will continue to perform their duties [despite the shutdown],” Steinbuchel said.