M.D. IPA is the largest Washington area "individual practice association" -- doctors giving care in their own offices for the set sum you or your employer pays.

Started in 1979 by several Montgomery County doctors, M.D. IPA now has 67,000 members in 550 employe groups and 1,200 participating doctors, a number of them shareholders -- part owners -- in the plan.

In this and most other IPAs, the doctors get paid so much a head per month for each patient on their list. If the plan profits -- attracting enough subscribers and not spending too much on hospital or specialist care -- the doctors can get a share.

But "in this plan," maintains Dr. John Ford of Silver Spring and Damascus, one of the founders, "we can practice just as we've always practiced. Fifty percent of my patients belong to this plan, 50 percent don't, and I treat them medically all the same."

Other area IPAs and the like:

*HealthPlus is the area's oldest IPA, founded in 1979 by the Prince George's County Medical Society but now operated by Sanus, a national for-profit corporation, and physician-shareholders. HealthPlus has 21,000 members in 300 employer groups and 900 participating doctors.

*Network, owned by an Arlington for-profit corporation, was launched in January 1984 and has 11,600 members in 300 employe groups and 1,000 participating doctors.

*CapitalCare is just being launched by National Capital Area Blue Cross-Blue Shield.

*Physicians Care is another new plan, being started by physician-owners.

*Aetna Choice has 12,000 members in 73 employe groups. Members go to any doctor they want for primary care -- Choice pays the fee -- but must choose from among 250 specialists (many at George Washington University).

*Yet another new player in the area medical game is yet another new sort of health plan, a PPO or "preferred provider organization." This is Health Point Preferred, owned by Provident Life and Accident Co. of Chattanooga, Tenn. Already active in Baltimore, Health Point is just starting to market in the Washington area, where 350 participating doctors are now available to employes of Health Point's first major customer here, Martin Marietta. Its workers may now go to a Health Point doctor for just a $5 payment -- or, if they choose, any other doctor and be reimbursed by traditional health insurance.