For four years and counting, Congress has been unable to approve long-term authority for the agency’s budgets and capital spending plans. Twenty temporary spending measures, some of them lasting just a few weeks, have come and gone. Last week, Congress again failed to resolve the impasse that has held up an agreement, including battles over subsidies for flights to rural airports and — something dear to the hearts of out-of-town lawmakers — adding more flights at Reagan National Airport near Washington.

So last week, Congress scrapped attempts to approve the 21st temporary spending plan before the last one expired on Friday — thereby shutting down a large part of the F.A.A. The agency stresses that it has enough money to keep airports open and planes safely in the air. But it cannot work on long-term projects. It has furloughed 4,000 employees, stopped work on construction projects employing thousands more and halted research on next-generation air traffic control systems. The F.A.A. is not some esoteric financial concept like the debt ceiling — an issue that has some lawmakers proclaiming the end is nigh while others bluster that it does not really matter. The aviation agency holds the lives of hundreds of thousands of travelers in its hands every day, overseeing the nation’s airports and the air traffic controllers who make sure that tens of thousands of flights a day take off and land safely.

 “It’s amazingly aberrant behavior on the part of our lawmakers that they haven’t been able to get a bill approved since 2007,” said Marion C. Blakey, president of the Aerospace Industries Association, who from 2002-7 was the F.A.A. administrator, the agency’s top official. The issue is not merely a question of whether the F.A.A. might have to delay some spending on little-used airports in the districts of powerful legislators. Their dependence on a stream of short-term F.A.A. allocations has led airports to have to bid out projects one small chunk at a time, raising costs and inconveniencing travelers.

“This is not a good way to do business,” Randy Babbitt, the current F.A.A. administrator, said in an interview. “It is a terribly inefficient use of the taxpayer dollar.” Without authorization from Congress, the F.A.A. cannot collect taxes on airline tickets that pay for much of its operations. The federal government is losing about $30 million a day from the loss of the ticket tax. For a Congress whose members routinely discuss the importance of adding jobs and constraining spending, an F.A.A. shutdown that lays off workers and makes projects more expensive would seem to go against common sense. Members of both parties and house of Congress blamed each other for the problem. “I was appalled that the House went through on its dangerous threats last week to hold the entire F.A.A. bill hostage to their politics,” Senator John D. Rockefeller IV, a West Virginia Democrat and chairman of the Senate Commerce committee, said on Monday.

Representative John L. Mica, a Florida Republican who is chairman of the House Transportation committee, shot back: “To put people back to work and restart F.A.A. programs, the Senate needs to adopt the F.A.A. extension passed by the House last Wednesday.” As they did in the two previous sessions of Congress, the House and the Senate each passed bills that would give the F.A.A. its long-term authorization. But they have been unable to reconcile their versions. One of the sticking points has been the Essential Air Service program, which pays subsidies to provide for regularly scheduled flights to rural airports that would otherwise be too unprofitable to operate. Each house wants to tighten the restrictions, but they differ on how to do it. Those services played a part in the failure of Congress to approve even a short-term spending plan last week. The 20 stopgap spending measures passed over the last four years included no extraneous changes in budgeted programs. This time, however, the House inserted language that would end subsidized service to small airports in Nevada and Montana, states represented by high-ranking Democratic senators, among others.

Another disagreement is over the number of long-distance flights that are allowed each day at Reagan Airport, which is the closest to Capitol Hill of the three major airports in the region.
Members of Congress from Western states want more direct flights from Reagan Airport to their home states. Members from Virginia, and some in Maryland, want to protect their constituents from the noise the additional flights would create. Those issues have been sticking points for years. A more recent disagreement is an ideological debate over how to administer union elections. Last year, the National Mediation Board, which settles labor disputes in the airline and railroad industries, adopted a rule saying that a vote by a company’s employees on whether to certify a union would be decided by a majority of those voting, rather than by a majority of employees eligible to vote. The change was supported by the two board members appointed by President Obama, and opposed by the lone Bush appointee. Republicans in Congress and many airline and railroad companies have criticized the change, saying it overturns decades of precedent. Democrats and labor leaders say it puts those industries on the same footing as unions in nearly every other industry in the country. The House F.A.A. bill contains a provision to repeal the rule. After failing last week to approve the most recent F.A.A. short-term reauthorization, many members went to the airport and flew home.