NAIROBI, Kenya (AP) _ The deformed faces of as many as 150 Kenyan youths are being radically improved by a U.S. medical team on a 10-day tour to repair cleft lips and palates.

The team, made up of volunteers for a 5-year-old Norfolk, Va.-based organization called Operation Smile, includes plastic surgeons, anesthesiologist s, a pediatrician, a dentist, three nurses, a speech therapist and some social workers.

Since arriving Sept. 9, the 19-member team has operated on as many as two dozen split lips and palates a day. It is scheduled to finish its work Friday.

''For the first few days here, there was noticeable skepticism about what we were - whether we were on an ego trip or here for humanitarian reasons,'' said Ron Godby, a 45-year-old dentist from Yorktown, Va.

''We're not here for ourselves,'' he said. ''We're here for the people.''

The team is working at the free government-owned and operated Kenyatta National Hospital, a medical complex with about 2,000 beds.

Dr. Mike Mbalu, Kenyatta's resident plastic surgeon, said Operation Smile would help clear up a backlog of patients awaiting surgery.

''We get about six new cases a week, making about 300 a year. Of the six, we can only admit two or three,'' he said. ''We're constrained because of shortages of staff and facilities. With Operation Smile, we feel that the number of cases left should be manageable.''

Most of Operation Smile's patients are young children whose mothers stay with them in one of two bare, high-ceilinged wards until it's time to operate.

Small faces stare from 42 metal cot-like beds lined along the walls under large windows in both wards. The children often cringe in fear as doctors examine them.

''In many societies they're treated as outcasts,'' said Steve Reynolds, a Nairobi representative for the Monrovia, Calif.-based World Vision, a Christian humanitarian aid and development group that helped facilitate Operation Smile's Kenya mission.

''We've found cases of kids who have been locked away, never develop any social skills and end up being terrified of people,'' Reynolds added.

''The parents, too, are punished,'' said Mbalu. ''Often mothers believe their children are born this way because they think they are being punished and have been bewitched.''

Clefts in lips and palates are congenital deformities that result in lips split up to and sometimes through the nose, and palates that have holes or are entirely missing, leaving the person unable to eat or speak properly.

''They also can have difficulty swallowing and breathing. As a result, we find that children with this problem are more malnourished than others in their age groups,'' Mbalu said.

Dr. Mike Vincent, a plastic surgeon at Bethesda Naval Hospital, in Bethesda, Md., said the U.S. team had to work under ''challenging'' conditions.

''The lights in the operating rooms tend not to be as good as we're accustomed to ... and we have no electric cautery (for stopping bleeding),'' said Vincent, who assisted in a July 31 operation to remove cancer from President Reagan's nose.

''But we feel good. Things are going well,'' he said. ''It's good to be able to come and do as much as possible and improve the lives of children.''

Since its founding in 1982, Operation Smile has sent an annual medical mission to the Philippines and repaired over 1,000 cleft lips and palates. This is its first venture into Africa.

A team also was sent to Liberia simultaneously with the Kenyan group.