DISTRICT SCHOOL officials say they must hire from 400 to 450 teachers per year through 1994. These will be needed to replace massive numbers of retiring teachers and to reduce class sizes. The city's residency requirement creates a severe problem here. The rule says that new city employees must take up residence in the District within 120 days of being hired. That will be particularly discouraging to new teaching applicants because of the city's shortage of decent and affordable housing.

The District's rental market has a vacancy rate of only 2.4 percent. That means new teachers must compete with everyone else for the roughly 4,200 apartments that are vacant and on the market at any given time. Waiving the residency requirement would give them more housing options and make a D.C. teaching job more attractive.

More competitive salaries would also help. Too often a very misleading statistic is used to compare teacher salaries. Federal statistics show that the average salary for a D.C. teacher is $33,990. But the D.C. average is so high because large numbers of teachers have reached the top of the seniority ladder. Over 60 percent of the city's teachers have more than 15 years of experience. Several began their careers in the 1950s.

For recruiting, the better benchmark is starting teacher salaries. The District -- which will need many more new teachers -- fares poorly. Beginning teachers in the D.C. schools this fall will have a pre-tax income of $19,116. That compares with $21,100 in Prince Georges County; $21,508 in Arlington; $21,620 in Alexandria; $22,000 in Montgomery County; and $22,000 in Fairfax County.

Compare that $19,116 salary with the old standard that says people should pay no more than 30 percent of their gross income on housing. That 30 percent is about $500 per month. On a typical day, the newspaper apartment listings showed that the city's average one-bedroom apartment rented for almost $600 per month.

The mayor and the D.C. Council should waive the residency requirement for teachers. Maintaining it -- and low starting salaries -- in a tight and expensive rental market would make it increasingly difficult to attract the best young teachers to the D.C. public schools.