The ailing 3-week-old infant abducted Thursday from Prince George's Hospital Center may die as early as today if he doesn't get medical care, according to his doctors and parents who issued an emotional, sometimes tearful appeal yesterday for his safe return.

Meanwhile, police said they believe whoever abducted the baby may have smuggled him out of the hospital in a white canvas Wilson brand sports bag that was missing from the hospital room. Prince George's County police said they had no other clues in the case.

The parents of Jeremiah Robert Thate, who was being treated for pneumonia, held a news conference yesterday and urged the abductor to return the baby or take him to a doctor for treatment.

Robert and Theresa Thate of Hyattsville sat close together, holding hands, before reporters in the gym of the Prince George's County Police Training Academy in Forestville. Robert Thate appeared calm; his wife cried through much of the news conference.

"The doctor said in the next 24 hours if he doesn't get care, he might die," said Robert Thate, 23, a cartographer for Greenhorne & O'Mara Inc. in Greenbelt. "Please do not compound your crime. Please release our son before it gets worse. Please do not dump him in a garbage can somewhere. I ask you to be compassionate to us and our child."

"I want him back," Theresa Thate said. "He may seem healthy now. But he won't stay that way."

Jeremiah, brought to the hospital Monday, was being treated for pneumonia in the right lung when someone cut or pulled an intravenous tube from the baby's arm that was feeding him antibiotics, and lifted him from a hospital crib.

The parents said they had left the room for a snack at the hospital canteen, and informed a passing nurse that they were leaving for a few minutes.

Doctors treating the baby said his condition could worsen during the next 24 hours and perhaps become fatal if he does not get medical attention. Doctors also expressed concern that if the intravenous tube was yanked from his arm or removed improperly, Jeremiah could bleed to death.

Police have no suspects or motive in the abduction, but now believe the baby may have been smuggled out of the hospital room in a white canvas gym bag with brown trim and the brand name "WILSON" on the side.

Police said the bag was used by Theresa Thate, who was staying in the room with the baby. Her clothes, which had been in the bag, were found in the room, but the bag was missing, said police spokesman Bruce Gentile.

Police also said they plan to interview a woman to whom Theresa Thate talked about the baby around 2:30 p.m. Thursday, two hours before Jeremiah was reported missing. The woman, about 35 years old, apparently walked by mistake into the room where Jeremiah and Theresa Thate were staying. The woman apologized and asked several questions about the baby, including his name and other personal information, police said.

Gentile said police know who the woman is but do not suspect her in the abduction. Police are interviewing hospital workers to find out if they saw any suspicious activity Thursday, and detectives are talking to friends and relatives of the Thates for any leads.

Gentile said that although police have no suspects, he said in other cases in which babies were taken from hospitals, the abductor usually was a childless woman or a mentally unstable woman. This is the first such abduction from a Prince George's hospital, Gentile said.

Last July, a newborn was taken "I want him back."

-- Theresa Thate

from her mother's arms in Arlington Hospital by a woman dressed in a hospital uniform, who said the baby would be returned after routine blood tests.

The baby was recovered a week later and Valerie M. Holbert was tried and found not guilty by reason of insanity. She was committed to a Virginia mental institution.

After the Arlington incident, several local hospitals improved security in their obstetrics wards, such as using new identification procedures for employes and visitors. Prince George's Hospital Center provided color-coded uniforms for nurses to eliminate confusion over who is a hospital employe.

Hospital Vice President Ronald W. Weitz said yesterday the administrative staff is reviewing all security procedures for possible improvements.