Gurgling, smiling and happily trying to stuff an alphabet block into her mouth, Nicole Brady, 8 1/2 months, was keeping up her end of a "dialogue" with Gloria Karp.

Karp, an education specialist and therapist, listened intently and reassured Nicole's mother that Nicole's non-specific "dadada" and "m-m-m" sounds were the forerunners of "Daddy" and "Mommy." Her "goo"--a more advanced sound because it comes from the back of the throat--signaled that Nicole's cognitive development was right on course.

Nicole's chatter, her reactions to a stranger (Karp), whether she crawled, could roll a ball, pick up a raisin and a report of her reactions to events at home, were part of a one-hour developmental assessment. The assessment by Karp was offered by Fairfax pediatricians Richard Todhunter and Russell Libby, who are among an increasing number of children's physicians utilizing the expertise of child-development specialists.

Nicole's mother had opted for the assessment, not because the doctors had spotted a problem or she was worried about her daughter's progress, but because she was curious.

"There's always something you can learn about your child that you have blindly overlooked," says Delores Brady of Fairfax as Nicole, her third child, played peek-a-boo and pat-a-cake (both developmental indicators) with Karp.

A developmental assessment is a series of screening devices or tests that can detect delays in physical (motor) and mental (cognitive) skills. Some assessments can detect social and emotional lags. The tests vary with the age of the child and can be tailored to newborns or adolescents.

For school-age children the tests are used to diagnose and evaluate a learning disability or serious functional problem. For infants and preschoolers, the lags that often lead to these problems can be detected early.

"If we can pick up developmental problems early, chances are they will be easier to correct," says Dr. Stanley Greenspan, chief of the Mental Health Study Center at the National Institutes of Mental Health.

"There is evidence that because the brain is growing most rapidly--to three-fourths of its adult size--during the first three years of life, an infant's or young child's recovery power ability to change and adapt may be much greater."

"If we get them under 2 years of age, we can reverse a lot of that stuff," adds Phillip Devore, a psychologist and administrative director of the Northern Virginia Diagnostic and Evaluation Center.

While comprehensive diagnostic assessments have been available through county, city and institutional programs for several years, these programs have been geared to children with known or suspected problems or at risk of developing them. That is beginning to change; developmental assessments that screen for symptoms are becoming available to the general public as part of well-baby care and parent education.

* In Northern Virginia, the Child Find offices of the public school systems are sponsoring a developmental screening "fair" through Friday. Parents who live in the area are encouraged to call their local Child Find office for a free-assessment appointment.

* The Regional Center for Infants and Young Children, a developmental evaluation, diagnosis and treatment center in Silver Spring founded by several NIMH researchers, offers well-baby developmental assessments at The Parent Place.

* Area physicians are beginning to include developmental screening as part of their routine infant checkups. (A separate hour-long assessment is $30 to $40.) Some doctors, like Alfred Scheuer, are specialists in a new pediatric sub-specialty: development.

"Pediatricians to varying degrees have always looked at development, but in the past it was a seat-of-the-pants approach--a very inaccurate estimation based on the practicioner's experience," says Scheuer, a Burke, Va., pediatrician and staff physician for the Regional Center.

"Today we have more tools and more standards of normative data so we can compare more precisely. It's only recently that there has been a push to educate and train practitioners so they could make reasonsible diagnoses in an office setting."

Scheuer believes that "all children need to be screened in some way so that the pediatrician has a sense of the child's abilities and areas of problems."

Pediatricians Todhunter and Libby asked education specialist Karp to run an assessment service through their offices because they were concerned that they were missing important information about their patients' progress.

"We'd ask the stock questions during a checkup," says Libby. "Is the baby sitting up? Is he standing? But given the time allotted for a checkup appointment, it was possible to miss things that now we can pick up."

"Parents seem reassured and at ease by having the assessment done here in a familiar setting," adds Todhunter. "We can tailor our discussions afterwards to the individual child's needs and parents' concerns."

The assessment is offered to all families when their children reach 9 months, 2 1/2 or 5 years of age (three developmental levels where specific skills should be apparent). Ninety percent of the families in their practice, says Todhunter, have utilized the service. Delays of varying degrees of severity have been found in about 10 percent of the children screened.

Children with serious delays are referred for further evaluation and therapy. For those children with less serious delays, Karp suggests at-home therapy in the form of stimulation, such as playing ball with an infant to encourage certain motor skills or reading to an infant to develop attention span.

When Carolyn Butler of Fairfax brought her 15-month-old son, David, in for an assessment, she realized "that while he was ahead in several areas, he was lagging in fine motor coordination."

In some situations, if a child with fine-motor lags doesn't get help, says Karp, "it could hurt him in school because he might not be able to do activities that other kids in school are doing.

"This could cause emotional problems about functioning on a level with his peers, and that might cause learning disabilities because he can't do the activities being taught."

After Karp assessed David, she suggested that Butler do specific infant-stimulation exercises with him at home. When David was reassessed three months later, Karp noticed major improvements.

"Some kids outgrow these lags, and we used to take a wait-and-see attitude," says Karp. "But now we don't believe that's good enough. Even if the child outgrows the problem without help, with this kind of intervention, what harm have you done?"

The assessments also can help parents think more deeply about their children.

Christine Buck, a Fairfax working mother, had her 4-year-old son Cliff assessed by Karp to see if his day-care situation was appropriate to his developmental level and whether, as a December baby, he should be pushed into kindergarten or held back.

"The test and interview," says Buck, "made me think about other criteria than whether he was bright enough to start school yet."

After Todhunter suggested that 11-month-old Lajune McCants of Alexandria be tested because she had been a premature baby, her mother Pauline was reassured by the results. "This is my first baby, and I'd been talking baby talk to her. I liked learning how to talk to her to increase her vocabulary and to read to her to increase her attention span. When she's ready to start school, she'll be more alert."

"Assessments like these," says Greenspan, "are for parents who want more information on a personal basis about their babies' individual characteristics and patterns.

"To the degree that parents are aware of the complexity of development, there will be greater alertness in the population to identify early on questions of difficulty and do something about them." Penelope Lemov is a Washington free-lance writer.