The nation faces a critical shortage of elementary and high school teachers over the next 10 years, educators predict, with an estimated 1 million new teachers needed by 1990.

The problem could reach crisis proportions, according to education analysts and teachers' union officials, because fewer college graduates are becoming teachers, elementary school enrollments are expected to increase, much of the teaching force is nearing retirement age and younger teachers are defecting to more lucrative fields.

"There is a teacher shortage crisis," said Bella Rosenberg of the American Federation of Teachers, AFL-CIO. "We tend to talk about it in terms of math and science teachers, but it's going to hit all fields."

"As the decade grows, the demand goes up but the supply is going way down," said Vance Grant, chief of the statistical information office at the National Center for Education Statistics. NCES figures show that the number of people receiving degrees in education was essentially cut in half between 1972 and 1982.

The shortage threatens to erode recent educational reforms while posing a painful dilemma for state legislatures. Pressed for the need to recruit more teachers, state politicians also must meet the competing public demand to raise teaching standards as a way to improve student performance.

Some school districts have begun hiring classroom instructors without traditional teaching qualifications. The Los Angeles Unified School District, for example, hired 167 "teacher-trainees" -- college graduates with no teacher training -- to meet their need for instructors last fall.

Education experts blame the impending crisis on a combination of demographic factors and changes in the labor market over the last two decades. A small "baby boomlet" of children born in the 1970s is entering the classrooms, and teachers of the post-World War II generation -- many of whom went to college on the G.I. bill -- are in their fifties and nearing retirement.

Increased job opportunities for women and blacks have deprived the teaching field of its most dependable pool of recruits.

"There was a time when women and minorities, if they wanted to enter a profession, had to go into teaching," Rosenberg said.

The teaching field is also plagued by massive defections by younger instructors, according to studies by the Rand Corp. and the American Enterprise Institute.

By most estimates, up to half of new teachers leave the job within five to seven years, usually expressing dissatisfaction. Even more discouraging to educators is the exodus of the most qualified teachers, those with the best test scores and school performance.

The pending crisis, coupled with the push for reform, has forced many states to pursue often contradictory policies, known in the education field as "screens and magnets."

"Screens" are policies aimed at "screening out" poor teachers. These include teacher-competency tests; stiffer professional requirements, such as prescribing certain college courses, and efforts to raise entrance and exit requirements at schools of education. Last year, 30 states had some form of teacher-competency test and a dozen more were considering them.

"Magnets" are policies to attract people to teaching: They include pay raises, forgivable loans and scholarships for students who want to study teaching, and proposals to use untrained college graduates to meet teacher shortages. Florida and New Jersey use these "alternative" teacher-certification plans. Some 28 states offer loans and scholarships.

"State policies are gradually changing from screens to magnets," said Stanford University Prof. Michael Kirst, former president of the California State Board of Education. "States are throwing out all sorts of magnets to see which ones work. It's like throwing out a fishing line to see what comes up."

"California is trying them all," he said. "We can't afford them all."

California -- like most Sun Belt states with growing populations -- will be among the first to feel the crunch, experts say. State education officials project that, with the growth of the immigrant population and migration from other states, school enrollment will expand by 600,000 by 1990.

At the same time, California officials see a need for 110,000 new teachers by 1990 -- in a total teacher population of just 170,000. In other words, the state will have to replace approximately two-thirds of its teacher force in the next five years. "It's a massive need for us," said Bill Honig, California superintendent for public instruction.

California's teacher population is aging rapidly. The state's teachers are five years older than the national average of 40, Honig and Kirst said. In Palo Alto, the average teacher is 50. San Francisco recently found that it had not hired a single new teacher who graduated from an education school after 1964.

The state has addressed the problem in several ways. Local school boards can declare an emergency because of the shortage, then hire any college graduate to teach as a special trainee -- as happened last fall in Los Angeles. Some cities, like Modesto in rural Stanislaus County, have even gone on the road to scout for talent.

"We see more and more localities going out recruiting," Honig said. "And they're going out East, is where they're going."

While state capitols have grappled with the problem through a variety of initiatives, the federal government has been less active. Congress last year, however, did approve a Talented Teacher Act, giving $96 million in scholarship aid to students of education, and separate programs to upgrade the teaching of math, science and "critical" foreign languages.

Educators said the "great unknown" in the teacher crisis is the "reserve army," the thousands of people with teacher training who have left the profession -- many of them women who left after marriage.

"Will they come back?" Kirst asked. "If so, under what conditions? There are just a lot of people out there who, on paper, are qualified to teach."