The shifting terrain for immigrants caught Mr. Medina and his wife, Ruth, unprepared, they said, because their first lawyer never notified them that an immigration appeals board had confirmed a deportation order against Mr. Medina in 2002. The lawyer had reassured them that his case was still proceeding.

Mr. [Benjamin Bratter] said a lawyer for the agency told him she was willing to file a joint motion to reopen the deportation case in favor of Mr. Medina, but was waiting for authorization. Instead, he said, Mr. Medina was pressed to sign travel documents in an effort to send him back to Guatemala immediately.

[Jorge] and Ruth Medina in 2000. Federal authorities are trying to deport him. (pg. B1); Ruth Medina in Nutley, N.J., with her daughters, [Raquel], 6, and Daniela, 9, and the Rev. [Brian Jordan], an immigrant advocate who has been trying to free her husband from detention and a deportation order. (Photo by Norman Y. Lono for The New York Times)(pg. B6)

Congress is still a few days away from establishing sweeping federal requirements for a driver's license, including proof that an applicant's presence in the United States is legal. But as Jorge Medina-Gonzalez discovered late last year driving from a Home Depot with a can of paint, the rules of the road in places like Nutley, N.J., have already changed.

Mr. Medina, 42, was close to home when two Nutley police officers stopped his Jeep Cherokee because of a broken taillight. They asked for his license and registration, then his Social Security number. In the few minutes it took them to search a national database in a curbside version of the kind of checks that Congress is about to require nationwide, the American life Mr. Medina had built over 13 years began to crumble.

Like many of the estimated 10 million illegal residents in this country, Mr. Medina -- who came here in 1991 to escape poverty and political violence in his native Guatemala -- has repeatedly tried to legalize his status through shifting rules set by Congress, and the delays of an overwhelmed immigration system. He stood before the police as a taxpaying Nutley homeowner with no criminal record, the father of two United States citizens, and a cook at a New York catering company that was sponsoring him for a green card.

But the computer search came back with a single message: immigration authorities, at one point, had ordered him deported. His driver's license became a one-way ticket to immigration jail, where he remains.

Supporters of the provision known as Real ID, which is being fine-tuned in a House and Senate conference committee this week, say it is primarily needed to keep driver's licenses out of the hands of terrorists and criminals. But immigrant advocates say one of its biggest effects will be to trip up workers like Mr. Medina, opening a trapdoor into a system of criminal penalties with few protections.

''The intention is to prevent hijackers and terrorists from getting licenses that would let them get on planes,'' said Benjamin Bratter, an immigration lawyer who is appealing an order of deportation entered against Mr. Medina in 2001, arguing in part that a previous lawyer had botched the case. ''But look at who gets caught up in this -- a guy like Jorge, a lay minister, a father of two. This can't be the intended result.''

That result, however, is welcomed by advocates for restricting immigration, who say Real ID will deter illegal immigrants by making it harder for them to use driver's licenses to open bank accounts, buy homes and put down roots.

An immigration judge ordered Mr. Medina deported in 2001 after denying his bid for political asylum, pending since 1993, saying that conditions in Guatemala had improved.

Mr. Medina's case highlights the way tougher licensing policies adopted over the last two years in states like New York and New Jersey have already converged with the 2002 decision by Attorney General John Ashcroft to add many civil immigration matters to the National Crime Information Center database, which is maintained by the F.B.I. and checked by the police even in routine traffic stops.

Pending court challenges in New York have slowed the effects of these changes, and temporarily halted the suspension of an estimated 300,000 New York licenses, most held by noncitizens. Real ID provisions, which are expected to be attached to a must-pass Iraq appropriations bill as early as next week, would most likely supersede the court challenges, and would require a vast expansion of the immigration records and national computer databases to be checked whenever anyone tries to get or renew a driver's license.

New Jersey is still phasing in a legislative overhaul of licensing that took effect in 2003, including a requirement that applicants show their presence is legal, according to Gordon Deal, a spokesman for the State Motor Vehicle Commission. A recent check by the commission found discrepancies between Social Security Administration records and the Social Security numbers provided by a half-million New Jersey drivers.

The shifting terrain for immigrants caught Mr. Medina and his wife, Ruth, unprepared, they said, because their first lawyer never notified them that an immigration appeals board had confirmed a deportation order against Mr. Medina in 2002. The lawyer had reassured them that his case was still proceeding.

''We put our last penny in this house,'' said Mrs. Medina, in the two-bedroom home they bought late in 2003, a step up from the one-bedroom apartment in Union City where they had been raising Daniela, now 9, and Raquel, 6. ''We were doing our life, like normal people.''

Normal, that is, for immigrants in the gray area occupied by families like the Medinas. Mrs. Medina, as a Honduran citizen, has only ''temporary protected status,'' renewed from year to year, that allows her to live and work here. Mr. Medina had been issued annual work permits for years, but saw one green card application derailed when his sponsor, the owner of Word of Mouth Foods, died unexpectedly about four years ago.

He started over with a new application, but his first lawyer failed to file the necessary papers until after Mr. Medina was stopped by the police .

The Rev. Brian Jordan, a Franciscan friar and immigrant advocate who visited Mr. Medina in immigration detention in Elizabeth last week, described the episode as an Orwellian descent into the unexplained.

''He was taken to the Nutley police station, put in a cell and was never told why he was being incarcerated,'' Father Jordan said. When immigration authorities had no agent available to pick him up, Mr. Medina was released, but told to report to an immigration office near Newark International Airport.

There, an immigration officer was reassuring, saying he had not reviewed the file but would call him in a few days.

A week later, when the officer asked Mr. Medina to come in, he and his wife went together, unable to reach their lawyer and confident that it was a routine check-in. Instead, the agent told Mr. Medina to hand over his belt and say goodbye to his wife: he was to be detained and deported.

Even after Citizenship and Immigration Services, an arm of the Department of Homeland Security, provisionally granted Mr. Medina's employer-sponsored petition in March -- with a push from Representative Charles B. Rangel -- Mr. Medina was still in detention, still fighting deportation.

Mr. Bratter said a lawyer for the agency told him she was willing to file a joint motion to reopen the deportation case in favor of Mr. Medina, but was waiting for authorization. Instead, he said, Mr. Medina was pressed to sign travel documents in an effort to send him back to Guatemala immediately.

When he refused to sign, immigration agents threatened him with criminal prosecution under an obscure 1952 federal statute that carries up to four years in prison for interfering with a deportation.

''There's an existing deportation order, and our mission in restoring integrity to the immigration system is enforcing the lawful orders of a federal immigration judge,'' said Manny Van Pelt, a spokesman for Immigration and Customs Enforcement. He said recalcitrant detainees were being prosecuted under the 1952 law.

After Mr. Bratter intervened, government lawyers decided not to prosecute Mr. Medina, said Michael Drewniak, a spokesman for the United States attorney's office in Newark. But that still leaves Mr. Medina facing deportation.

''The little one just doesn't really understand what's going on,'' said Mrs. Medina, who has sold her car. ''She just wants her daddy back.''