District residents who need orthodontic treatment may be hard put to find this specialized dental care in their own neighborhoods unless they live in Northwest, where about three-fourths of the city's orthodontists practice.

Both the D.C. Dental Society and the Department of Human Resources report that the overwhelming majority of orthodontists have offices in North-west although the two agencies cannot agree on the precise numbers.

Dental Society statistics show that 22 of the District's 28 orthodontists practice in Northwest, three are in South-east, two in Northeast and one in Southwest. The Department of Human Resources records show that only 17 orthodontists practice in the District but they reflect the same lopsided distribution, with 11 in Ward 3 in North-west; three in Ward 2, which covers parts of all four sections; one in Ward 5 in Northeast; two for whom no addresses were listed; none in Ward 1 and 4 in Northwest and a small area of Northeast, and none in Wards 6, 7 and 8, in Southeast and Northeast.

Spokesmen for the dental society and DHR could not explain the discrepancy.

The geographic imbalance also exists among dental practices generally in the city. Of more than 500 dentists, about 400 are located in Northwest, according to DHR. Only 10 practice in Anacostia's Ward 8.

In discussing orthodontic care, Dr. Joseph Payne, chief of the DHR medical assistance unit, estimates that although as many as 90 percent of all children may require some "intervention" to correct irregularities in teeth alignment, most people don't seek treatment because of the high costs and lack of information.

You may be surprised when the dentist suggests that the youngster "should see an orthodontist." But many orthodontic problems are not visible to the unpracticed eye and, left unattended, they sometimes lead to dental, gum and bone trouble in adult-hood. So the safest route is to have them checked.

It may turn out that minimal treatment will be required to straighten your offspring's teeth. And in some fortunate cases, the verdict will be to let nature take its course.

Selecting an orthodontist isn't always easy.

"It's like choosing a lawyer, a diamond agent or a physician," says one D.C. orthodontist. "There just aren't any advance guarantees that he's the one for you."

But consumer advocates and practitioners themselves agree that taking the time to shop for a reputable orthodontist pays off. The D.C. Dental Society (686-0817) can provide names of specialists in your area, although Federal Trade Commission regulations prevent them from discussing fees.

Family dentists should be able to recommend orthodontists with whose work they are familiar. Friends can be a source of information in describing their experiences with various specialists.

Quality of care is the most important factor in choosing an orthodontist, but there are other considerations. Despite the uneven distribution of specialists throughout the District, it does help if older children can reach their orthodontist on their own since they will have about a dozen oppointments a year if extensive treatment is required.

Find out which orthodontists have weekend and evening office hours to cut down the time young patients have to miss from school for office visits.

Orthodontic treatment is expensive and newcomers to Washington will find that fees here tend to be higher than in other parts of the country.

Treatment over a two-year period for a patient wearing full appliances or braces on the upper and lower teeth, plus headgear, will usually run between $1,700 and $2,400 in the District. This does not include tooth extractions or regular dental maintenance, and orthodontists are quick to say the figures could go up if a patient does not cooperate in treatment or if the problems are unusually severe.

Recognizing the damage costly orthodontic care can do to many family budgets, most orthodontists try to work out reasonable billing schedules that call for a 10 to 30 percent deposit and then monthly payments spread over several months or even years.

Consumer advocates advise that fees and payment schedules should be discussed before treatment begins to avoid misunderstandings. Moreover, treatment procedures and all costs should be put in writing. Find out what might not be included such as emergency visits or lost or broken appliances.

Some dental insurance plans now include orthodontic care, but premiums are expensive. Medicaid does not cover treatment.

The dental schools at Howard and Georgetown universities are the only clinics in the District to offer orthodontic care at lower rates, from one-half to two-thirds the costs of private care. However, Howard's caseload won't allow taking on new patients, except on a consulting basis, for two to three years. Georgetown will accept a small number of patients if their orthodontic problems suit the teaching needs of the dental school.

No other low-cost, or free, orthodontic care is offered in the city for low-in-come residents, according to officials of DHR and the two dental schools.

No matter to whom you go, the orthodontist should be able to explain the problems, the need for treatment and the proposed corrective procedures in clear language you understand. If you're not satisfied, don't hesitate to get a second opinion. The patient's records can be forwarded to another orthodontist.