From left, Ricky Campos, 23; Katye Hernandez, 22; and Rachelle Robertello, 18, front, rally with other members of Casa de Maryland outside the White House after Obama announced a policy to offer legal status to some undocumented immigrants under the age of 30. (Jacquelyn Martin/AP)

President Obama has just opened a floodgate of opportunity for young illegal immigrants in the United States, but could it squeeze the aspirations of legal Americans in the process?

Across the nation Friday, immigrant advocates and Hispanic youth groups hailed Obama’s decision to offer legal status to some undocumented immigrants under 30 as a watershed in U.S. immigration history and a long-sought victory for ambitious youths denied a chance to realize the American dream.

“I thank God for this day. It has changed my whole life,” Jorge Acuna, 19, a college student in Silver Spring who came to the United States with his family as a child, told a cheering crowd outside the White House on Friday afternoon, minutes after Obama announced the new policy. Last spring, the community college student was nearly deported to his native Colombia. Now, under the amnesty, he will be able to pursue his degree in engineering.

But opponents of illegal immigration warned that the policy could create significant new competition for jobs and university slots at a time of nationwide recession and numerous states’ efforts to curb public spending.

“I see a tidal wave coming,” said Brad Botwin, president of Help Save Maryland, a group that opposes legalization for undocumented immigrants. “Half of our college graduates today can’t find jobs, and the unemployment rate for high-school-aged Americans is extremely high. This is unfair to U.S. citizens and legal immigrants who are out there struggling to get ahead.”

Residency not provided

Under the new policy, as many as 1.4 million undocumented immigrants under age 30 will be able to apply for the amnesty, allowing them to work and attend college legally. To be eligible, they must have been in the United States for five years, have no criminal record, and attend high school or college or be a military veteran.

The policy does not provide permanent legal residency, but it protects those who qualify from being deported and gives them a chance to renew their new status every two years. It also does not grant any public benefits, such as Medicare and Medicaid. Federal law already grants all undocumented immigrants the right to a public-school education and emergency hospital care.

The new policy could entail additional costs for administration and enforcement, however, and put pressure on state systems of higher education to meet growing demand for slots.

But it could also bring new revenue. Many illegal workers are paid in cash, and taxes or other costs are not deducted. One congressional study found that the Dream Act, a stalled proposal to grant legal residency to young immigrants who graduate from high school and attend college or join the military, would add $2.3 billion in tax revenue over 10 years.

“Texas and California will definitely benefit from this,” said Marielena Hincapie, executive director of the National Immigration Law Center in Los Angeles, adding that the two states have large populations of Hispanic immigrants who will now be able to open businesses, hire people and earn more.

Advocates for the change said it will create a more lawful atmosphere in immigrant communities and reduce the fear of deportation, which often prevents people from reporting crimes or seeking help with problems. But critics predicted that it would have the opposite effect, proving difficult to enforce and encouraging more illegal immigrants to use false identification documents to fit within the amnesty’s legal requirements.

It was not immediately clear how the policy would dovetail with state laws and policies on illegal immigration. In the absence of a broad federal mandate, states have passed a variety of laws ranging from the relatively lax to the extremely strict. In the first three months of 2012, more than 860 bills and resolutions concerning immigration were introduced in state legislatures.

California, Texas and eight other states have laws giving in-state tuition benefits to illegal immigrants. Maryland passed such a law, but it has been stalled by legal challenges. The new federal policy does not address this issue, however. At the other end of the spectrum, Arizona and Alabama have passed tough laws barring illegal immigrants from a range of activities and allowed police to check their legal status. Other states have passed laws to limit various types of public benefits available for illegal immigrants.

“The first thing that will make a difference to me is that now I can drive legally,” said Victor Palafox, 20, a Mexican immigrant and high school graduate who was visiting Washington from Alabama on Friday. “It gives me my humanity back.”

Immigration advocates as well as critics said the new policy is far from an adequate substitute for an overhaul of the entire federal immigration system. The issue is highly emotional and partisan, and lawmakers have repeatedly failed to agree on a broad policy to deal with the estimated 11.2 million illegal immigrants in the United States.

“Due to congressional inaction, we have seen a lot of laws passed at the state level that in many cases only add chaos,” said Clarissa Martinez, an official of the National Council of La Raza in Washington. “Where the administration is justified and able, they should intervene, as they have done in this case. But it only intensifies the need for Congress to act.”

The most significant and contentious aspect of the new policy is that it automatically grants hundreds of thousands of people in their teens and 20s — most of them from Mexico and Central America — the right to work in the United States. Many may have already been working, but as undocumented laborers they often had to accept low wages and poor conditions.

“For hundreds of thousands of young people, the immediate effect will be that they can exhale and go out and look for a job,” said Gustavo Andrade, an official of the pro-immigrant group CASA of Maryland.

Effect on low-wage jobs?

But Steven Camarota, a researcher with the nonprofit Center for Immigration Studies in Washington, said that the Obama administration was not taking into account the new measure’s probable impact on competition for jobs at the low end of the economic scale, where chronic unemployment is highest. Among Americans with less than a high school education, he said, the jobless rate is 13 percent.

“It doesn’t seem the administration is considering the cascading consequences,” Camarota said. “What does this mean for unemployed Americans who will be competing for jobs with a million-plus people who can now apply for work authorization? Is this really a good idea?”

Staff writers Krissah Thompson and Peter Whoriskey contributed to this report.