Edward Wyatt / New York Times News Service

WASHINGTON — After dealing with the debt crisis, Senate negotiators tried and failed Tuesday to end a stalemate over temporary financing for the Federal Aviation Administration, leaving 4,000 agency employees out of work and relying on airport safety inspectors to continue working without pay.

The partial agency shutdown, which began July 23 and is likely to continue at least through Labor Day, has also idled tens of thousands of construction workers on airport projects. Dozens of airport inspectors have been asked by the FAA to work without pay and to charge their government travel expenses to their personal credit cards to keep airports operating safely.

Air traffic controllers and airplane inspectors, who are paid with separate accounts, have continued to work, but workers who oversee research on aviation systems, grants for airports and facilities and operations equipment have been furloughed.

Ray LaHood, the transportation secretary, said he believed that passenger safety was not at risk.

“No safety issues will be compromised,” LaHood told reporters on a conference call. “Flying is safe. Air traffic controllers are guiding airplanes. Safety inspectors are on duty and are doing their job. No one needs to worry about safety.”

The House began its August recess Monday night, and the Senate followed Tuesday, leaving little hope for a resolution until Congress returns in September. President Barack Obama, in remarks after the Senate’s passage of the debt ceiling bill, urged Congress to break the impasse, which he described as “another Washington-inflicted wound on America.”

The impasse centers on disagreements between Republicans and Democrats over a program that subsidizes commercial air service to rural airports. But behind the scenes, a larger fight has been taking place over federal rules on labor elections in the airline industry.

Randy Babbitt, the FAA administrator, said in a conference call with reporters Tuesday that the agency was depending on the “professionalism” of airport safety inspectors to continue their work without being paid, because their jobs are paid for with money that is awaiting congressional authorization.

Those inspectors are the primary individuals responsible for ensuring that commercial airports comply with federal regulations. They also support runway safety action teams, oversee construction safety plans, investigate runway incursions and ensure that corrective action is taken on safety discrepancies.

“The reason they are out on the job is because of the risk to operational safety or life and property,” Babbitt said. “We can neither pay them nor can we compensate them for expenses. We are depending and living on their professionalism at this point.”

It is unclear how long the inspectors can continue to pay the bills for their own travel and hotel expenses. Typically, each of the roughly 40 regional inspectors travels to up to five airports in each two-week period, FAA officials said.

When FAA financing expired last month, the agency also lost the ability to collect taxes on airline tickets. Those taxes amount to about $30 million a day and are paid into a trust fund that pays for much of its operations.

The House passed a bill last month that would extend FAA financing through Sept. 16 and allow it to continue collecting the ticket tax. Congress has passed 20 such temporary spending bills over the past four years, in part because it has been unable to agree on a larger, long-term authorization of the agency’s budget and capital plans.

But the House temporary bill also would end $14 million in subsidies that provided commercial airline service to 16 rural airports. The law was written in a way that appeared to single out for closing airports in the states of prominent Senate Democrats, including the majority leader, Harry Reid of Nevada.

Democrats argue that Republicans are trying to save a few million dollars at the expense of the ticket tax, which would generate roughly $200 million a week, or close to $1 billion while Congress is on recess.

Rep. John Mica, R-Fla., chairman of the House transportation committee, said in a statement that the rural air cuts were intended to reduce wasteful spending, like the subsidies of more than $3,700 a passenger that paid for air service in Ely, Nev., that benefits fewer than 500 passengers a year.

“Those 4,000 FAA employees have been furloughed so some in the Senate can protect their own political pork,” Mica said.

Reid said Republicans were using the rural airport issue as cover for an effort to change a recently instituted federal labor regulation that made it easier for unions to organize at airline companies.

The new regulation, instituted by the National Mediation Board, requires an employee vote on labor representation to be approved by a majority of those voting. Previously, the rule required a majority of all affected employees, meaning that employees who failed to vote were counted as “no” votes.