THE FIRST GRIM word came three months ago, but not until this week's delivery of dismissal notices to 350 elementary school teachers did the shock hit the city's classrooms. Many of the newer members of faculties were steeled to accept the worst, but among others who have been teaching in the same communities for five or six years, there was bitter dissappointment, anger and frustration.

This is just the start of something big: next week, an undertermined number of junior and senior high school teachers and 45 assistant principals will be handed their papers as well -- in what officials say is the largest employee layoff in at least seven years.

Given the city's money shortage and a declining school enrollment, there is no question that dramatic cuts in the number of teachers were necessary, though many may quarrel with the method of cutting back and number of cuts. Because seniority is the criterion for determining layoffs, along with some consideration for military service, any connection with teaching is purely coincidental. In the elementary schools, there also is no connection between the specialties of those fired -- math or English -- and those still left. How or if the compu ters will shake out any of these school-to-school discrepancies before fall is anyone's guess; equally unavailable as yet is any information concering which of the remaining teachers will be shifted around the system to even out the numbers.

Plenty of people -- and not just cynics -- will wonder whether these drastic actions are merely part of a budget charade in which severe cuts of front-line jobs are threatened as a way of mobilizing public protest to lift spending ceilings or of cushioning the blow of smaller cuts. But School Superintendent Vincent E. Reed is not known for playing games; the math test that he is facing calls for proposing ways to cut tens of millions of dollars from a system in which 88 percent of the spending is for salaries.

There are other steps that can reduce the severity of the eventual teacher cuts: a sensible closing and selling of unused or underused buildings, additional reductions in administrative staff and -- for those 11 paid members of the school board with their staff that is costing a good $929,000 a year to run -- a solid dose of their own fiscal medicine.

Whatever happens, the sad fact is that those who suffer most from all this uncertainty -- the teacher shifts, the bigger classes, the elmination of classes in foreign languages, music, art and whatever is next -- will be the poorest families, those who have no options. Their voices will become even more faint as others bail out. That is why Dr. Reed continues to press for one important project aimed at preserving and someday maybe even enlarging the public school constituency: a high school with a strong academic cirriculum that could offer the best possible college preparation for any city student willing and able to keep up -- and that could lead to similar changes at every other public school as well.