Hopes, doubts vie as US girds to enforce new immigration law. Employer sanctions and amnesty are the key elements to be tested

Federal officials are gearing up for the most sweeping change in United States immigration law in more than two decades. On Monday, Dec. 1, it will become unlawful for any American employer to hire a foreign national who is in this country illegally.

The new law was designed to slam the door on millions of illegal aliens pouring into the US.

At the same time, officials are putting together plans to grant amnesty to millions of aliens, mostly from Mexico, who entered the country unlawfully prior to 1982.

The new law, passed after years of debate in Congress, was a compromise between those who wanted to halt illegal immigration and those concerned about violating the rights of Hispanics and other minority groups.

Experts are uncertain whether the law will work. George W. Grayson, author of ``The United States and Mexico: Patterns of Influence,'' calls it ``the most deeply flawed legislation that has been passed in recent memory.''

Immigration experts and federal officials have several concerns:

The sanctions against those hiring illegal aliens may not work. Heavy fines and jail terms are provided for employers who willfully hire illegals. But unless America's employers voluntarily cooperate, there will not be adequate manpower to police the law.

Amnesty for illegals may turn into a rubber stamp. No one is sure how many illegals are in the US. Millions may step forward to claim legal status, as provided under the law. The government could be buried in paper work. Experts are concerned that most applications for legalization will merely be rubber-stamped by an overworked federal bureaucracy, and that cases of fraud will abound.

Amnesty could encourage more illegal immigration. Word of the amnesty will quickly spread. Millions of additional illegals may be encouraged to come to the US on the assumption that another amnesty will be granted in a few years.

Despite these concerns, there is little doubt among immigration experts that the new law will have a tremendous impact on many sectors of American society.

Doris M. Meissner, the former acting commissioner of the Immigration and Naturalization Service, says industries that use illegals could be drastically affected. Those include such sectors as construction, restaurants, and the garment industry. The major exception will be agriculture, which won an exemption to the crackdown on the use of illegal alien labor.

Ms. Meissner noted at an immigration conference this week at the College of William and Mary in Williamsburg, Va., that employers will have plenty of time to adjust to the new law. There will be no enforcement of the hiring ban for the first six months. Then, during the next 12 months, only warnings will be issued. Only after that 18-month break-in period will Washington get tough.

Paul R. Verkuil, president of William and Mary, says the new law presents a paradox for the aliens: ``If you can prove that you have been in this country illegally since 1982, you can stay here legally.''

Dr. Verkuil notes that illegals have lived here only by avoiding the normal paper work of American life: paycheck stubs, rent receipts, income-tax returns. Yet those are just the kind of evidence they now need.

Like others, Verkuil expresses great concern about fraud. He notes that the government plans to use volunteer agencies and churches to run the initial check on most of the applications for amnesty and that ``the most important organization in this field in the Catholic church.''

Yet some Roman Catholic officials have been very active in seeking amnesty for illegals, even to the point of civil disobedience, Verkuil observes. He worries that there will be a great temptation on the part of the Catholic Church and other advocates of immigration to ``prove that people qualify.''

While millions of illegal aliens will qualify for amnesty, millions more will not. Their future remains in doubt. In theory, they will be forced to leave. They will not be able to get a job, once the ban on hiring is enforced. But experts doubt that there will be a mass exodus of illegal aliens. The hiring ban applies only to new employees, so illegals who fail to qualify for amnesty, but who already hold jobs, can remain in place.

Thousands of other illegals who don't qualify for amnesty are expected to remain a part of the underground economy, working for substandard wages, paid in cash, and kept off the books of their employers. Although not ideal, these conditions may be better than they could find at home.