The lawyers who defend the nation’s poor in federal courts across the country are grappling with budget cuts they say will decimate their offices, delay criminal cases and jeopardize the fairness of the criminal justice system.

The cuts have already forced some offices of federal defenders to lay people off, and many are planning to force staffers to take off six weeks or more without pay over the next six months. Even a Supreme Court justice has expressed concern that cuts could pressure the system and result in criminals running free.

The cuts, amounting to roughly 10 percent of this year’s budget, come in a program seen as the flagship for public defenders and as the nation marks this month’s 50th anniversary of the landmark Supreme Court decision Gideon v. Wainwright, which guaranteed that criminal defendants will be provided with a lawyer if they can’t afford one.

While federal prosecutors have been notified by the U.S. Department of Justice that they may be furloughed for up to 14 days, those cuts are not yet final. Federal public defenders, though, say cuts to their offices are virtually certain.

“It’s important that people who don’t have any power and any voice have people to speak for them,” said U.S. District Judge Catherine Blake of Maryland, who helps oversee the federal defenders program for the judiciary. “You never know when you might need the 6th Amendment.”

Defenders and court officials alike said some people will be held in prison longer while they await trial, costing taxpayers money. Justice Stephen Breyer testified this month before a House appropriations subcommittee that some people could be wrongly convicted while the real culprits remain free. Those who do not receive adequate representation could then appeal their convictions, costing the courts time and money.

In many districts, defenders said, staff members who sometimes work six or seven days a week are demoralized and worried about paying their mortgages, college tuition for their children and staggering student loans. Miriam Conrad, federal defender for Massachusetts, New Hampshire and Rhode Island, said some staff members have asked if they can take second jobs to pay the bills, something she has never seen in 21 years working in the office.

Several defenders warned of a slow-moving disaster that will get worse as the months wear on and delays pile up. They also worried that this year’s furloughs are not the end, and that even as the government brings more complex and time-consuming prosecutions such as mortgage fraud, they will be forced to lay more people off because of an appetite for cost-cutting in Washington.

Some federal courts have said they will not hear criminal cases on one day per week, or are considering such a plan, because of the planned furloughs of defenders and potential furloughs of U.S. marshals and prosecutors.

Ron Sullivan, a professor at Harvard Law School and director of its criminal justice program, said the cuts raise constitutional concerns.

“Average, everyday citizens should care because the quality of justice experienced in America could potentially diminish with these cuts,” he said. “Most Americans, in my view, believe that everyone has a right to a fair trial. When people have lawyers that are either under-resourced or ill trained, they do not get a fair trial.”

Michael Nachmanoff, federal defender for eastern Virginia, said his office was notified just a few weeks ago of the magnitude of the cut, which must be made up before Sept. 30. A little more than half is due to the automatic budget cuts known as the sequester. The rest is a cut for the fiscal year of the budget for the federal judiciary, which funds the federal public defender system.

Nachmanoff’s office has represented high-profile and time-and-money-intensive cases, such as Sept. 11 conspirator Zacarias Moussaoui and Somali pirates.

In some cases, the people he represents provide valuable information to help the government, Nachmanoff said. But when the wheels of justice are turning slower, that could hurt such investigations.

If public defenders can’t take a case because they don’t have the staff, the person will instead be assigned a private lawyer, who charges the government $125 per hour, far more expensive than what it costs a public defender.

“You pay them $125 per hour every hour that they work on the case. If they have to drive three hours because (their client is) in remote detention, the taxpayer’s paying for that. It’s crazy,” said Jon Sands, defender in Arizona and chair of the Defender Services Advisory Group, which advises the federal judiciary.