"I think this is important work," said Dr. Richard P. Meier, an assistant professor of linguistics and psychology at the University of Texas. "It's been suggested that all children pass through a regular sequence of milestones in speech acquisition, from simple cooing early on, to structured babbling at eight months, to the first word at about 12 months. This work gives us a new dimension of how language matures."

Dr. Marilyn M. Vihman, who is doing research on language acquisition at Rutgers University in New Brunswick, N.J., said the latest results offered further proof that babbling is a crucial step in language deveopment. "You'll see the emergence of babbling at the same age in any infant who has been exposed to language regardless of other things, including intelligence," she said. "Babies babble regardless of whether the language spoken at home is English, Japanese, French or, it seems, sign language." Videotaping Infants

Dr. Petitto and her graduate student, Paula F. Marentette, videotaped five infants at ages 10, 12 and 14 months. Two of the infants were deaf children of deaf parents who use American Sign Language to communicate, while the other three were hearing offspring of hearing adults. The researchers analyzed every hand gesture of the infants and compared the two groups.

They found that the hearing children made many hand gestures, but that the gestures never became organized or repetitive. By comparison, the deaf babies soon began showing evidence of using about 13 different hand motions over and over again. Nearly all of them were actual elements of American Sign Language: gestures that do not in themselves mean anything, but have the potential to indicate something when pieced together with other gestures.

Sign languages are structured much like any spoken language, Dr. Petitto said. Distinct gestures and hand shapes are the equivalent of syllables, and thus must be presented in a series to assume any sense. Reinforcement From Parents

She believes that the deaf parents noticed the nascent efforts of their children to communicate through signs and began reinforcing the gestures, just as normal parents talk back to and reinforce their babbling infants by turning the babble into words, for example, by saying "dadadada . . . Daddy."

But there was idiosyncratic taste at work as well. Just as one hearing baby may prefer to say "babababa" while another fastens upon "gagaga," so one of the deaf infants tended to make her gestures in front of her torso, while the other deaf baby performed his hand signs around his head and face.

The deaf babies could make noise, but they did not babble vocally like the hearing children.

Dr. Petitto said that the new work also supported the theory that the basic rhthym of all languages was the same, building upon a pattern that alternates consonants and vowels. Although the analogy is only approximate in sign language, the deaf babies did alternate between mobile gestures, which are thought to be somewhat vowel-like in their rhythms, and static hand shapes, the rough equivalent of the consonant.