On January 31, Antonia Estrella received a desperate call. After five years in immigration detention centers in Alabama, Georgia, and Louisiana, her son, Franklin Grullon, said he had been told his time was up. Immigration officials had informed Grullon, a legal permanent resident who pleaded guilty 10 years ago to drug and robbery charges, that he would be deported on the next flight to the Dominican Republic.

But at the 11th hour, the government granted a temporary reprieve. Grullon – and probably thousands in similar situations – now has the opportunity for a waiver hearing, one that may allow him to stay in this country legally.

“Now there’s a little hope,” Ms. Estrella, a Bronx resident, said in Spanish. “Now they’re saying, ‘Yes, he’s going to have his day in court.’ “

When Grullon, 39, who immigrated legally at 16 and is the father of two American citizens, was convicted in 1995, other noncitizen criminals in his situation were eligible for relief from deportation. Relief was a chance to present evidence to immigration judges that they should be allowed to stay in America, evidence such as rehabilitation and ties to the community.

When the immigration laws were overhauled in 1996, however, that opportunity was taken away for thousands. A broad category of crimes known as aggravated felonies now triggers automatic deportation.

Those laws were applied retroactively. Thus, when Grullon was released in 2000, he was immediately placed in deportation proceedings.

This fall, however, the Justice Department issued a new rule, and immigrants like Grullon, who have not yet been deported, have been given a second chance. The change was based on a Supreme Court decision four years ago that it was unlawful to apply the change retroactively.

For thousands, it’s too late. The Justice Department is not allowing those already deported to apply for the waiver. More than 500,000 noncitizens with criminal convictions, many of whom would have been eligible for the waiver, have been deported since the new laws went into effect in 1996.

Others will not hear about the waiver in time: The opportunity to apply runs out this April 26. In October, the Justice Department posted notices in the Federal Register and sent out a press release, but immigration lawyers said the information is not trickling down to immigrant offenders who need to hear it.

The New York State Defenders Association’s Immigrant Defense Project, a nonprofit group, is scrambling to get the word out that some immigrants who, before 1997, pleaded guilty to a crime, can seek a waiver.

“Every other day, our hotline mailbox gets filled because of people calling,” a staff attorney of the Defense Project, Benita Jain, said.

For many of them, however, the rule change came too late.

“Most people who have been calling us have a loved one who was deported wrongfully, and there’s not a lot we can say to them,” she said. “For people who were deported, the government’s position is they can’t come back to apply for the waiver, even though they were wrongfully deported.”

Another problem disturbs a New York University School of Law professor, Nancy Morawetz, who helped prepare the plaintiff’s brief in the Supreme Court case. She said the government is not doing enough to inform immigrants from countries with which America currently has no repatriation agreements, such as Cuba, Vietnam, and Laos. Many have been released from detention because the government will not be able to deport them in the foreseeable future, but they are unaware they should apply for the waiver to prevent future deportation in the event of a shift in bilateral relations. Such a shift recently took place with Cambodia, where America is now able to deport immigrants convicted of crimes.

“What I think is a huge problem is that they tell people there is a time limit, and they simply assume people will know what they are supposed to do. It’s a very complicated piece of law,” Ms. Morawetz said. “When the government makes a mistake, they have a clear responsibility to fix it, and that’s a responsibility they’re clearly reneging on in these regulations.”

The Justice Department said its response reflects standard policy.

“This is consistent with what the Department of Justice has done in other cases where individuals were given an opportunity to seek relief. But at the same time, the matter is not left open indefinitely,” a spokesman for the department, John Nowacki, said.

Advocates of increased restrictions on immigration see the waivers as providing a new loophole to let the worst type of immigrants remain in the country.

But for Franklin Grullon’s mother, Ms. Estrella, “212(c),” the name of the waiver and a number she loves to rattle off in Spanish, is the last hope for her son. Ever since his conviction, she said, she has contended he was innocent and was tricked into pleading guilty.

Now, with a stack of court papers almost as tall as she is and more than 170 family members and friends signed on to support his waiver application, she is optimistic that she will keep her son in American and then clear his name.