The D. C. Hospital Commission, after a year-long nationwide search, has chosen as medical director of D.C. General Hospital a 35-year-old pediatrician who has been running one of the hospital's programs in Southeast Washington.

Dr. Lawrence B. Johnson, a native of Camden, N.J., today becomes the $75,000-a-year medical director of the city's only public hospital, taking responsibility for all patient care at the institution.

The post has been vacant since February 1981, when Stanford A. Roman resigned because he was frustrated by the slow pace of change at the hospital and financial problems besieging it.

D.C. General's administrator Robert Johnson said the post was advertised in major newspapers and medical journals for almost a year, but that several finalists hesitated over the salary and were not willing to move to the expensive Washington area to lead a public institution.

Robert Johnson said that "everybody who interviewed Lawrence Johnson put him in the same league" with other potential candidates.

D.C. General has been neighborhood doctor, nurse and pharmacist to much of Washington's indigent population for half a century. The hospital staff treats 11,000 inpatients a year, and handles 180,000 emergency room and outpatient visits annually--more than any other hospital in town.

The hospital also is a training ground for medical students, interns and residents from Howard and Georgetown universities. The director is head of the hospital's teaching staff, and both universities contribute stipends totaling $18,500 to the director's salary, in addition to his base pay of $56,500 from the hospital.

Like many other public hospitals, D.C. General has faced overcrowding, understaffing and limited funds, which at times have diminished its reputation.

The hospital's massive, aging building, which houses 557 beds, is currently undergoing major renovations, and after a lengthly battle with the city has been granted permission to lease a highly sophisticated X-ray machine called a CAT scanner, an important but expensive piece of diagnostic equipment doctors have long felt is vital to the hospital.

"My major interest is with examining the role of the public health system . . . and D.C. General is in a position to provide a wide range of services that other hospitals don't have the time, interest, patients or money to do," Lawrence Johnson said in an interview Saturday. "The challenge of trying to do that in the face of very hard times is one that has attracted me to the position."

He says his plans for the hospital include saving money by collaborating with other area hospitals in providing some services; developing a group practice for the hospital's senior physicians and dentists; and finding a way to "personalize" services at the hospital so that patients will have their own primary physicians.

Johnson directed the hospital's Southeast Washington Primary Care Network from August 1980 until last January, and has served as acting director of the hospital in recent weeks. The Southeast program was designed to coordinate services and funds among private and city-run health clinics in Wards 7 and 8. But the program never really got off the ground because of cuts in federal funding.

Johnson is a resident of Columbia, Md., and will not be required to move into Washington, because physicians are exempt from the city's residency law. Married and the father of one daughter, he graduated from New York's Columbia University College of Physicans and Surgeons in 1972 and trained at Harlem Hospital and at a public hospital in Cleveland.

Before coming to Washington, he was director of the Comprehensive Child Health Program and Emergency Services at Children's Hospital Medical Center in Boston.