If Congress fails to come to an agreement, the government shutdown that officially began at 12:01 a.m. Saturday would continue indefinitely. Hundreds of thousands of federal workers would be furloughed, affecting a wide range of government programs.

Share of Employees Who Would Stay Home Agency Total employees Furloughed Share of employees Housing and Urban Development 7,800 7,500 96% Environmental Protection Agency 14,400 13,700 95% Education 3,900 3,700 95% Commerce 47,900 41,600 87% Labor 15,400 12,800 83% Interior 70,400 56,600 80% Treasury 88,000 48,500 55% Health and Human Services 81,900 41,000 50% Defense (civilian workforce) 740,000 370,000 50% Transportation 55,200 20,500 37% Justice 114,600 19,500 17% Social Security Administration 63,200 10,400 16% Homeland Security 241,400 31,200 13% Veterans Affairs 377,000 15,900 4% Note: Current data for the State, Energy and Agriculture Departments were not immediately available.

Source: Agency contingency plans

Critical services that protect “human life or property,” like air traffic control, and programs like the United States Postal Service that have alternate funding sources would continue.

Here are the outlooks for major federal agencies and some consequences of the last government shutdown, which lasted for 16 days in October 2013:

Housing and Urban Development

Most of the nearly 8,000 employees would be furloughed, but the agency would continue essential services like emergency housing for the homeless and new loan endorsements for single family homes.

Loans to develop or rehabilitate rental units went unprocessed.

Environmental Protection Agency

Most of its nearly 14,500 employees would be furloughed, according to the agency’s contingency plan. On Friday, however, the agency’s administrator, Scott Pruitt, said that E.P.A. has sufficient resources to operate through next week even if government financing expired and that all employees should plan on working next week.

Inspections at about 1,200 water, hazardous waste and chemical sites were halted.

Evaluations of potential health impacts of new industrial chemicals were discontinued.

Reviews of pesticides for adverse effects on health and the environment were stopped.

Education

Most of the department’s nearly 4,000 employees would be furloughed. Other than financial aid support, most of the department’s activities would come to a halt.

Commerce

Of the department’s nearly 48,000 employees, 90 percent would be furloughed. Work would stall across a wide swath of scientific and economic agencies, including the National Oceanic Atmospheric Administration, the Census Bureau and the International Trade Administration, while activities like fisheries management, patent processing and climate observation would continue.

Important monthly reports on trade, retail sales and construction were not released.

Some technology exports were delayed.

Labor

More than 80 percent of its 15,000 or so employees would be furloughed. Most of the department would be closed, but unemployment compensation would continue.

Some 1,400 inspections to prevent workplace fatalities were delayed.

Investigations to enforce workplace protections were delayed.

Monthly employment and price reports were not released.

Interior

More than three-quarters of the roughly 70,000 employees would be furloughed. Unlike with previous shutdowns, national parks would remain open, but some services that require staffing, like campgrounds and full-service restrooms, would not operate. Smithsonian museums and the National Zoo would be closed beginning on Monday.

Drilling permit applications were not processed.

National parks and the Smithsonian closed.

Data on natural disasters could not be gathered.

Treasury

More than half of the 88,000 or so employees would be furloughed. The Internal Revenue Service would exempt more employees from being furloughed than it normally would during a shutdown because it is tax filing season.

There was a much larger furlough of 80 percent of employees.

Export certificates for alcohol were not issued.

The I.R.S. could not verify data for private-sector lenders.

Tax refunds were delayed.

Implementation of financial sanctions against countries like Iran and Syria were hampered.

Health and Human Services

Half of its nearly 82,000 employees would be furloughed, including a vast majority of staff members at agencies that provide grants. Agencies with a substantial direct service component, like the Indian Health Service, would remain mostly open. Medicare would operate “largely without disruption,” according to the Health and Human Services contingency plan, and health care exchange activities would continue.

Approval of medical devices and drugs was delayed.

Flu season surveillance and monitoring were cut back.

New patients were prevented from enrolling in clinical studies.

Head Start programs temporarily closed their centers.

Food safety inspections were delayed.

Defense

The furlough would apply only to about half of the department’s 740,000 civilian workers, but military personnel also would not be paid unless Congress voted to pay them (it did in 2013).

Contracts with small businesses dropped by almost one-third.

Thousands of hours were spent developing and implementing contingency plans and restarting full operations.

Transportation

Less than half of its 55,000 or so employees would be furloughed, leaving operations like air traffic control and hazardous material safety inspections largely intact.

Aircraft purchases and deliveries were delayed.

The United States Merchant Marine Academy closed for nearly three weeks. The latest guidance said that the academy would now remain open in a shutdown.

Justice

More than 80 percent of the department’s 115,000 employees would be allowed to work through a shutdown because they have national security, law enforcement and criminal justice responsibilities.

Social Security Administration

Social Security recipients would continue to receive their benefits. Most of the agency’s 63,000 employees would continue to work.

Homeland Security

A small share of the department’s 241,000 employees would be furloughed, including those who perform planning, research, policy, regulatory and training activities. Nearly all Customs and Border Protection; Immigration and Customs Enforcement; and Transportation Security Administration employees would remain at work.

Veterans Affairs

Nearly 96 percent of the agency’s roughly 377,000 employees would continue to work. V.A. hospitals would remain open but functions like education assistance and case appeals would be delayed.

Progress in reducing the backlog of disability claims stalled.

Support for military service members who were transitioning to civilian life was delayed.

State

The department has not released estimates for how many employees would be furloughed. According to a memo, passport services would continue, though passport offices in federal buildings affected by the shutdown could be closed.

Energy

Current furlough data for the agency was not immediately available, but 69 percent of workers were furloughed in 2013.

National Nuclear Security Administration labs and plants and also nuclear cleanup sites likely lost weeks of productivity.

Agriculture

Nutrition programs including food stamps (SNAP) and the program for women and children (WIC) would continue. Current furlough data for the agency was not immediately available.