As part of the immigration-reform bill that President Reagan signed this month, the federal government is promising to help states and communities pay for the social services that hundreds of thousands of illegal aliens are expected to qualify for as they become legal residents. The immigration law earmarks $1 billion over each of the next four years to help pay the public assistance, health, and education costs of what some estimates put at more than a million new legal residents.
That is good news for the cities and counties that for years have paid, with little federal help, to treat the emergencies, deliver the babies, and educate the children of undocumented aliens.
But across the country, and especially in areas where large numbers of illegal aliens are now concentrated, local officials are uncertain whether the federal dollars will be enough, and are skeptical about just how much of the money will ever reach local coffers.
They note that states and the federal government itself will take their share of the money first. And they doubt that the reform will greatly curtail illegal immigration - thus leaving them open to continued pressure on their services.
``If nothing more, I'd call the money the beginning of the recognition process about the costs and pressures we're facing down here,'' says Pat O'Rourke, the county judge (chief administrator) in El Paso County, Texas. ``It won't solve our problem, but it's a start.''
Much of the uncertainty over how far the federal money will go stems from the fact that no one knows how many aliens will qualify - or apply - for legal status.
``No one knows, and you'll hear the same thing all across the country,'' says Nancy Wittenberg, refugee-program administrator for Florida. ``Even our guesses wouldn't be very good.''
The Congressional Budget Office (CBO) has ventured a guess that 1.4 million illegal aliens, plus 250,000 agricultural workers, will qualify for the new law's amnesty from deportation.
Simply put, any illegal alien who has lived here continuously since before Jan. 1, 1982, or any agriculture worker who worked at least 90 days between May 1985 and May 1986, will qualify for temporary resident status.
The CBO also believes that the $4 billion to be laid out over the next four fiscal years will be sufficient to cover state and local governments' social-service costs, even after the federal government skims off about $1 billion to pay for food stamps, social security insurance, and certain medicaid costs for the newly legal residents.
But immigration experts and local officials maintain that such figures can be only guesses, since no one knows how many undocumented aliens, accustomed to hiding their status, will apply for legal residency.
``A lot of people just won't qualify, and many others won't risk coming forward only to be told they don't meet the criteria,'' says Leo Chavez, a research associate with the Center for US-Mexico Studies at the University of California at San Diego.
Florida's undocumented population did not grow significantly until 1984, according to Ms. Wittenberg, so it would appear that the state may not see much of the federal money.
Mr. Chavez believes for another reason, as well, that local officials have little reason to fear that their costs will burgeon because of a newly legalized population. He says the great majority of illegal aliens are young working males who make little use of any public assistance. They come to this country to work, he says, ``not to sit back and collect welfare.''
Even so, he believes that those undocumented aliens who do use publicly supported hospitals for emergencies and births, and public schools for education, will continue to do so.
And that means local governments will continue to bear the burden of the illegal population.
Chavez notes that studies in California and Texas have shown that illegal aliens pay more in taxes than they draw from the system in services. The problem is that they tend to pay federal and state taxes, but few local taxes, where they do cost money.
Los Angeles County is a case in point. Of the 2 million undocumented aliens counted in the 1980 US census, 32 percent resided in Los Angeles. Most of them work, pay state and federal income taxes and social security withholding, but do not own property and so do not pay county property tax.
The county estimates that it paid about $270 million in ``nonreimbursable'' funds for services for illegal aliens last year, much of it in the county hospital system. According to Mark Tajima, a legislative analyst with the Los Angeles County Chief Administrative Office, the county's hospitals deliver each year between 18,000 and 20,000 new American citizens to illegal aliens.
In Texas, El Paso County officials - who last year sent President Reagan a bill for $10 million to highlight local health-care costs for illegal aliens - say they will pay $12 million this year. And in Laredo, school officials say nearly 4 percent of the district's 22,000 students are illegal aliens.
Some immigration analysts question such statistics, pointing out that documentation of schoolchildren or hospital emergency patients is not always thorough, and that cities and counties stand to gain by puffing up the cost of services to illegal aliens.
Partly as a result of incessant protests from border counties, medicare will begin in January to pay part of local public hospitals' costs for emergency service to illegal aliens.
But Judge O'Rourke says that even with new medicare money and whatever portion of the $1 billion in federal compensation his county sees ``trickle down,'' county taxpayers will still be paying more than their share of social-service costs for both newly legalized residents and illegal aliens.
Others, such as Mr. Tajima, say they doubt Congress will actually come up with $1 billion for each of the next four years for newly legalized residents. They note that, under pressure from the federal budget deficit, Congress is already having trouble finding money for programs for the elderly and other domestic programs.
And even if Congress does, neither the new residents nor illegal aliens will be less numerous in 1991 when the funding stops, they say. ``We don't want to bilk the federal government,'' O'Rourke says, ``but we can't take care of the problem on our own, either. We all expect to see [illegal] immigration stay up.''