A 20-year-old Northeast Washington woman pleaded guilty yesterday in D.C. Superior Court to the kidnaping of a day-old infant last summer from George Washington University Hospital.

Sharon V. Rector, of 1130 Morse St. NE. agreed to plead guilty to the July 6, 1979, kidnaping of Walthon C. Lee Jr. in exchange for the government's promise to drop a burglary charge in connection with the incident at sentencing.

Rector, who will be sentenced on May 13, could receive from 20 years to life in prison for the kidnaping conviction.

The baby was taken from his mother's hospital room when she left to respond to a telephone call. The mother, Linda Jackson, said that a female caller told her she should go to another part of the hospital to sign some papers.

Jackson said she found no one at the location she was directed to by the caller. When she returned to her room, the infant was missing.

D.C. police and FBI agents searched for the baby for three days. Finally, acting on a telephone tip on July 9, police arranged a meeting at Fort Dupont Park, where the baby was returned by Rector's brother Donald.

The government contended in court yesterday that, Rector had visited the hospital before the kidnaping. She developed a "feeling of effection" for the infant and used her knowledge of hospital procedures to lure the mother away from the child, the government contended.

Rector changed the infant's clothing before she left the hospital, then caught a ride to the F Street Mall. From there she hailed a cab, which drove her to her mother's Northeast Washington home.