By Ayesha Rascoe

WASHINGTON (Reuters) - The Obama administration, in its final weeks, plans to ease the legal obligations on prisoners to pay for child support while they are locked up, targeting practices that critics say can saddle ex-convicts with crippling debts.

The regulatory changes, if put in place, would give President Barack Obama something more to show for his efforts to reform the U.S. criminal justice system, a legacy issue for the Democrat whose time in office ends on Jan. 20.

As the first black president of a nation that incarcerates a disproportionately large number of black and Latino men, Obama has made it a priority to address problems that make it difficult for released inmates to reenter society.

A White House official, speaking on condition of anonymity because the new rules are not final, expressed confidence they would be completed before Obama leaves office.

The rules would require that prisoners be allowed to lower the amount of child support they pay in prison, with the goal of preventing large debts that inmates struggle to repay after release and that can lead to reincarceration.

Some Republican critics have said such a change would let parents flout their financial responsibilities. Republican Speaker of the House of Representatives Paul Ryan last year introduced a bill to block the administration from making such a change. The bill did not become law.

A Republican House aide told Reuters the administration's initiative would amount to a "backdoor effort" to avoid the legislative process.

Criminal justice reform was supposed to be an area where Republicans and Democrats could find common ground in 2016, but legislative efforts have stalled.

As a result, the administration needs to move forward on its own where it can, the White House official said.

"We are always happy to sit down and talk with Congress, but at some point we have to move forward with what we know we are legally permitted to do and what is right," the official said.

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Child-support programs require absent parents to send money, usually to the spouse who has custody, to help raise their children. For prisoners who have little or no income, regular child-support payments can accumulate into unmanageable debts.

Just ask Glenn Martin. As a young father, he went to prison for six years for armed robbery. While in prison, his child support payments were increased to $400 a month from $50 a month, even though he only earned about $40 a month.

    When he was released, Martin told Reuters he faced a $50,000 civil judgment for back child support, including interest. He said he tried to get that changed, but judges said state law did not permit modifications for incarceration.

Martin went on to found a prison reform group, JustLeadershipUSA. "We have two decades of evidence that says that being tough just hasn't worked," he said.

"What it has done is further criminalize the people we should be trying to move into the labor market."

Most states have changed their laws so that child support payments for prisoners can be modified, but 14 states still do not allow it or place major obstacles in the way.

The Obama administration issued draft regulations in late 2014 that would require states to allow prisoners to modify their child support court orders, while also requiring state courts to set orders based on prisoners' "actual" income.

States run their own child support enforcement programs, but Washington sets nationwide standards and reimburses states for 66 percent of expenditures on the programs and provides incentive payments to states based on meeting certain targets. 

The final version of the draft rules, still not public, was sent to the White House for review in July.

Supporters say the changes will help reduce prison populations by preventing ex-convicts from accruing debts that make it difficult for them to find legitimate jobs and increases the likelihood they could face jail time over unpaid child support payments.

A 2010 administration survey found 51,000 federal prisoners had child support orders, with almost 29,000 of the prisoners behind on payments. The average amount owed was nearly $24,000.

"The child support system as it exists today in a lot of ways has become ... a major driver of mass incarceration," said Rebecca Vallas, managing director of the Poverty to Prosperity program at the Center for American Progress, a Washington think tank.

(Editing by Kevin Drawbaugh and Andrew Hay)