President Clinton's recent speech on immigration at Portland State University was an excellent policy statement, but it raises some troubling questions that are almost universally swept under the rug.

He was quite right in praising the immigrants' contributions to American society and in denouncing prejudice against people 'with new accents.'

Is it possible, however, to have respect and compassion for present immigrants and still raise questions about the conse-quences of future immigration?

Despite the ravings of some racist fanatics, immigration is not a racial problem; it is a popu-lation problem. It is projected to be a principal cause of population growth.

Is it 'immigrant-bashing' or simply common foresight to ask what would be required for a "Is it possible to have respect and compassion for present immigrants and still raise questions about the [environmental] consequences of future immigration?"doubled or tripled or quadrupled population? What about jobs, schools, parks, housing, air quality, open space, farmland and food production, transportation and infrastructure of all kinds?

We need more information about the carrying capacity of this state and the U.S. - the limits set by natural resources.

In California the most conspicuous resource in short supply is water. In drought years, this state does not have enough water available for the present population at the current rate of use.

Water conservation and recycling - both urban and agricultural - could make more water available, up to a point. But all possible belt-tightening measures could not indefinitely accommodate a continually growing population.

How much water could be imported to California - from the Columbia River, from the Yukon, from the Mississippi, and at what cost? What population could any such sources accommodate?

The ocean offers an unlimited supply, but desalting sea water and pumping it uphill would require colossal amounts of energy at a time when fossil-fuel consumption must be diminished.

Nuclear power has seemingly insuperable problems of safety and radioactive waste disposal. Solar energy on a large scale would require vast amounts of land to collect sunlight. How much of the state would be covered by the collectors and how much energy would they supply?

Questions like these must be answered not only about water but about the limits of the other natural resources that are under population pressure - fertile soil, forests, wildlife, fisheries, open space, and the services furnished by ecosystems that are vital to the economy.

Population growth is not the only source of resource depletion. Possibly half or more of our water - and other resources - is wasted by careless consumption.

We need to learn how many people California could sustainably support if we ran a tight ship, eliminating waste while maintaining standards of living.

Population, of course, is a global problem. There is an urgent need to offer family-planning methods, education and economic aid to developing countries in sufficient amounts to help them reduce population growth and build prosperous, sustainable economies that could diminish migrations.

But that's a very long-run prospect. In the meantime, we must plan for the local impact. The population of California has increased ten times within the lifetime of this writer. Can we anticipate another tenfold increase?

We have in this state some top-drawer research universities capable of developing detailed pictures of California at various future levels of population and consumption.

Only with this kind of information can we have rational public discussion of immigration and population growth. But there will be no possibility of answers until we start asking the right questions. Let's get them out from under the rug. TSCThe National Research Council had been asked by the Immigration Reform Commission, headed by the late Barbara Jordan, to examine the demographic, economic and fiscal consequences of immigration. As this chart shows, they project that the non-Hispanic "white" population of the U.S. will shrink from 74 percent of the population in 1995 to 51 percent in 2050. The biggest factor propelling population change is immigration, now mostly from Latin America and Asia.