AIR TRAVEL

Federal air traffic controllers would remain on the job and airport screeners would keep funneling passengers through security checkpoints. Federal inspectors would continue enforcing safety rules.

INTERNATIONAL TRAVEL

The State Department would continue processing foreign applications for visas and U.S. applications for passports, since fees are collected to finance those services. Embassies and consulates overseas would continue to provide services to American citizens.

MAIL

Deliveries would continue as usual because the U.S. Postal Service receives no tax dollars for day-to-day operations. It relies on income from stamps and other postal fees to keep running.

RECREATION

All national parks would be closed, as would the Smithsonian museums, including the National Zoo in Washington. Visitors using overnight campgrounds or other park facilities would be given 48 hours to make alternate arrangements and leave the park. Among the visitor centers that would be closed: the Statue of Liberty and Ellis Island in New York, Independence Hall in Philadelphia, Alcatraz Island near San Francisco and the Washington Monument.

HEALTH

New patients would not be accepted into clinical research at the National Institutes of Health, but current patients would continue to receive care. Medical research at the NIH would be disrupted and some studies would be delayed. The Centers for Disease Control and Prevention would be severely limited in spotting or investigating disease outbreaks, from flu to that mysterious MERS virus from the Middle East.

FOOD SAFETY

The Food and Drug Administration would handle high-risk recalls suspend most routine safety inspections. Federal meat inspections would be expected to proceed as usual.

HEAD START

A small number of Head Start programs, about 20 out of 1,600 nationally, would feel the impact right away. The federal Administration for Children and Families says grants expiring about Oct. 1 would not be renewed. Over time more programs would be affected. Several of the Head Start programs that would immediately feel the pinch are in Florida. It's unclear if they would continue serving children.

FOOD ASSISTANCE

The Special Supplemental Nutrition Program for Women, Infants and Children, known as WIC, could shut down. The program provides supplemental food, health care referrals and nutrition education for pregnant women, mothers and their children.

School lunches and breakfasts would continue to be served, and food stamps, known as the Supplemental Nutrition Assistance Program, or SNAP, would continue to be distributed. But several smaller feeding programs would not have the money to operate.

TAXES

Americans would still have to pay their taxes and file federal tax returns, but the Internal Revenue Service says it would suspend all audits. Got questions? Sorry, the IRS says taxpayer services, including toll-free help lines, would be shut as well.

LOANS

Many low-to-moderate incomes borrowers and first-time homebuyers seeking government-backed mortgages could face delays during the shutdown. The Federal Housing Administration, which guarantees about 30 percent of home mortgages, wouldn't underwrite or approve any new loans during the shutdown. Action on government-backed loans to small businesses would be suspended.

SCIENCE

NASA will continue to keep workers at Mission Control in Houston and elsewhere to support the International Space station, where two Americans and four others are deployed. The National Weather Service would keep forecasting weather and issuing warnings and the National Hurricane Center would continue to track storms. The scientific work of the U.S. Geological Survey would be halted.

HOMELAND SECURITY

The majority of the Department of Homeland Security's employees are expected to stay on the job, including uniformed agents and officers at the country's borders and ports of entry, members of the Coast Guard, Transportation Security Administration officers, Secret Service personnel and other law enforcement agents and officers. U.S. Citizenship and Immigration Services employees would continue to process green card applications.

MILITARY

The military's 1.4 million active duty personnel would stay on duty, but their paychecks would be delayed. About half of the Defense Department's civilian employees would be furloughed.

PRISONS

All 116 federal prisons would remain open, and criminal litigation would proceed.

VETERANS SERVICES

Most services offered through the Department of Veterans Affairs will continue because lawmakers approve money one year in advance for the VA's health programs. Veterans would still be able to visit hospitals for inpatient care, get mental health counseling at vet centers or get prescriptions filled at VA health clinics. Operators would still staff the crisis hotline and claims workers would still process payments to cover disability and pension benefits. But those veterans appealing the denial of disability benefits to the Board of Veterans Appeals will have to wait longer for a decision because the board would not issue any decisions during a shutdown.

WORK SAFETY

Federal occupational safety and health inspectors would stop workplace inspections except in cases of imminent danger.