A senior Homeland Security official said that deportations would be canceled case by case. While many immigrants in those cases will be eligible for work permits, he said, employment authorization will come only after a separate process.

The immigrants will remain in a sort of legal limbo, not vulnerable to deportation but with no positive immigration status, which can be conferred only by Congress.

But White House officials and Congressional Democrats said they expected the measures would lead to relief during the coming year for virtually all young illegal immigrants facing deportation who might have won legal status under a bill called the Dream Act. A proposal to benefit illegal immigrant high school graduates who came to the country before they were 16, it failed in the Senate last year.

Mr. Guerra, now 27 and living in Indiantown, Fla., is one of those immigrants. He said he came to this country to escape a violent gang in Mexico. His lawyer, Richard A. Hujber, said Mr. Guerra’s efforts to straighten out his legal status went wrong because they were originally mishandled by an accountant claiming falsely to be a lawyer.

In recent years, even though he was undocumented, Mr. Guerra has been a Florida leader of the illegal immigrant student movement, helping to organize a protest walk by four students to Washington and a mock university held by students wearing mortarboards on Capitol Hill.

“That was so big to me, all these students organizing a school so we could go without our papers,” Mr. Guerra said. If he can obtain a work permit, he and Mr. Hujber said, he could be legally eligible for the first time to apply for financial aid that would allow him to continue his religious studies.

The administration’s announcement also had an immediate impact on a case in Denver, where an immigration judge on Friday postponed the deportation of Sujey Pando, a lesbian from Mexico legally married in Iowa to an American from Colorado, Violeta Pando. Although federal law does not recognize same-sex marriages, administration officials said they would consider same-sex spouses as “family” in their review of deportation cases.