David Carliner states ("Aliens Are People, Too," op-ed, Aug. 5 ) that if illegal aliens in the United States total 6 million, then they represent 2.5 percent of the population, "hardly of crisis proportions." In my view, neither the long-nor the short-term impact of millions of illegal aliens is reflected in a static, overallpopulation percentage. Even the larger percentages that illegal aliens represent of the adult population in certain geographical areas may not adequately convey their true impact.

Illegal immigration is adding hundreds of thousands per year to U.S. population, concentrated in a few heavily impacted states. Illegal aliens have competed for jobs with an unknown portion of America's 7.5 million unemployed, burdening not only those displaced workers and their families, but also the taxpayers, who must shoulder the cost of welfare and unemployment benefits. American society as a whole then suffers the social tension, crime and other problems related to such unemployment. In addition, the presence of illegal aliens likely reduces GNP per capita (a measure we make of "average prosperity") with the associated social and political consequences. Illegal immigration also contributes to the creation of "foreign" enclaves in certain areas, creating the risk of separatism. Not only do many illegal aliens then fail to learn English and otherwise assimilate, but they slow the assimilation of legal aliens from the same country of origin. Pluralism--our most distinctive national trait--suffers.

Currently, only a fraction of illegal aliens are apprehended. Of these, almost all are merely sent back to their home country. In 1980, over 900,000 apprehensions occurred, yet considerably fewer than 1 percent resulted in prosecutions. This minute disincentive is outweighed by the high probability of obtaining a U.S. job. If the jobs are made unavailable through an employer sanctions system, then the major incentive for most aliens to gain illegal entry will no longer exist.

Carliner asserts that a verification procedure could be easily overwhelmed with counterfeit documents. This would not be true if the system required that the basic, counterfeitable documents that prove citizenship or legal alien status be first presented for screening to a government agency rather than to employers. Whether the procedure that is ultimately chosen utilizes a card or not, it would not be substantially more burdensome than the existing requirement that a Social Security number be obtained and presented to the employer.

Carliner claims that discrimination would result against those who "are thought to 'look or speak foreign'." On the contrary, a new verification procedure is sorely needed to avoid such discrimination. If an employer is fully protected by following the minimal presentation procedures, then there will be no uncertainty as to whether a particular applicant can be "lawfully hired."