The District public schools have known for several years that a teacher shortage is looming. More than half of the D.C. system's teachers will reach retirement age by 1993. More than a quarter of D.C. teachers -- including many of those with the best credentials and test scores -- are considering leaving teaching in the city because of low salaries, the low prestige of teaching and work conditions, a recent survey found.

Now D.C. Superintendent Floretta D. McKenzie has proposed steps to recruit better teachers and keep the best ones in city schools. The plan, to be considered by the school board in coming months, could cost anywhere from $6 million to $43 million, depending on how greatly salaries are increased.

Without incentives and better recruiting tactics, the District "may not attract the number and quality of teachers it needs," McKenzie said. The need is keen: 84 percent of the out-of-state applicants who were offered District teaching jobs last year rejected the offers.

To attract good teachers, McKenzie has proposed to provide tuition assistance to District college students who agree to teach in city schools for two years for each year of aid. Also, the District would match the starting salaries of suburban school systems, which now pay new teachers several thousand dollars more than the District's $19,500 annual starting pay.

And the District would give new teachers relocation allowances of $500 to $1,500, along with loans of up to $1,000 to help with the high cost of setting up in the District, where all new employes are required to live. And the school system would provide direct help in finding housing in the city, a difficult task that many new teachers say has dissuaded them from staying in their positions.

Finally, the system would seek legal authority to exempt some categories of teachers from the city's residency requirement on the basis that those posts cannot be filled from the pool of District residents.

Finding good teachers who are willing to work in inner-city schools is expected to become ever more difficult, McKenzie said. A recent survey of education majors found that the majority said they would not teach in large urban school districts.

In the District, which has a mostly black teaching staff and a student population that is predominantly minority, attracting good minority teachers is essential, the superintendent said.

To keep the best teachers and prevent them from leaving for higher pay and better work conditions in the suburbs, McKenzie proposes to offer renewal bonuses of $500 after two years of service and $1,000 per year for teachers of retirement age who stay on.

Also, she would guarantee summer jobs to new teachers who are performing well and would encourage the best teachers to stay fresh by offering tuition aid of 75 percent in exchange for an extra two-year commitment to the schools.