WHETHER YOU CHOOSE to vote or to stay home this fall is your business. Getting out the vote is the job of candidates and other civic organizations. We would merely note this month that if you choose to leave your options open for September, now is the time to make sure they will be; unless you are registered in the next few weeks, your choice will have been made for you already.

According to the Metropolitan Washington Council of Governments, there are approximately 2.2 million residents 18 years old and over, and of these, only 1.4 million are registered. For September's voting in the region, the registration rolls will close in the early days of August. Anyone not on the lists after that will be ineligible to vote. Period. Decisions to be made in September could include the selection of party nominees for seats in the Virginia House, while in Maryland, party candidates will be chosen for scores of state and local offices.

In the District, as residents know, the September Democratic primary is, in effect, the election for mayor, council chairman and most council members. And in the District, as many voters have learned to their horror in the past, the registration rolls haven't been all they were cooked up to be in terms of accuracy. A private computer team and a reorganized elections staff have been working to clean up these records, but the elections board urges that people check now to verify their registration. That may not guarantee that all will be well at the polls--but it's an important precautionary step.