Last year 78 missing children were returned home thanks to Child Find, and, in part, thanks to Gloria Markfield. A longtime Great Neck resident and retired businesswoman, Ms Markfield is now president of the board of Child Find, a national not-for-profit charity whose mission is to locate missing children through investigation, prevent child abduction through education, and resolve incidents of parental abduction through mediation.

''We're the organization of last resort,'' says Ms. Markfield, explaining that some cases of missing children are actually ''outside the purview of police or FBI'' (non-custodial kidnapping, for example), and Child Find can help. Hundreds of searches are conducted each year.

When a case of a missing child---missing, runaway, or abducted---is called in to Child Find, the organization goes into action, circulating posters throughout known areas such as schools, shops, and neighboring homes, contacting family and friends near and far. Posters also go into the neighborhood where the abductor may be from. Remaining in touch with key contacts such as the school principal, Child Find begins investigating, searching Social Security numbers and public information sources.

Child Find, says Ms. Markfield, does the work that parents may not have the skills, the funds, nor the emotional energy to pursue. And, for sure, Child Find can ''gear up'' much quicker.

Very often the missing child has been taken by a friend or relative, sometimes by one parent's ''significant other.'' So it's important to teach children a ''clue word,'' which should be changed weekly. This really works, Ms. Markfield stresses. She offered the example of a Great Neck child who is still home with the custodial parent, thanks to a clue word. The non-custodial parent showed up at school to take the child; the clue word was not used and so the child notified the school principal. The custodial parent was called, and a possible abduction was averted.

Watching young children, keeping in contact with older children and keeping lines of communication open are all important, says Ms. Markfield. As well, children should be ''educated'' about safety, ''they should be warned.'' In response to parents who fear frightening their children, she says, ''You don't have to frighten young children, but you should warn them as to possible dangers of abduction and kidnapping...It's an ugly fact of life, but it's a fact of life....I'd be afraid not to warn them.''

And Child Find offers help, and brochures, teaching parents how to teach their youngsters to be safe---keeping children close and watching them; code words; teaching children to keep away from strangers, explaining the abduction problem; teaching children it's okay to scream and run away from someone making him or her do something he or she does not want to do.

Sometimes problems are solved, or abductions averted, when a Child Find mediator speaks to both parents, and finds a solution that ends, or prevents, an abduction. ''Prevention, of course, is best,'' says Ms. Markfield, ''Children are damaged in abduction---emotionally or physically.'' There are skilled mediators available all over the country.

As for runaways, Child Find tries to ''bring them to safety,'' even if safety is not home, but as a ward of the court.

Gloria Markfield became involved with Child Find five years ago, when, as CEO for Catalyst (working with major corporations to advance the role of women in management) she first began helping Child Find work through financial problems. Sensitive to the issue of missing children since the Etan Patz incident, she began volunteering, as does a huge network of professionals working pro bono.

''The problem of missing children has increased with more split families and people being more mobile,'' says Ms. Markfield. She is quick to add that the ''most gratifying'' part of the whole job is, of course, when a child is found. ''I've actually been there (at headquarters in New Paltz) when a child was found...One day an investigator came in singing 'Found a peanut, found a peanut'...It's just unbelievable.''

Child Find is often confused with other agencies. The pictures on the milk cartons were from Child Find, but this has been discontinued because some parents found that it frightened their children, and not many were found through that method, according to Ms. Markfield. ''It did raise the issue in the minds of adults, but we do not want to frighten children.''

In addition to finding children, mediating, and educating children and parents though literature, Child Find also holds seminars and speaks to groups. And while most of the funding (90 cents of every dollar) is spent on all of the Child Find programs (there is only a small paid staff), a great deal is spent actually locating missing youngsters.

Child Find was just rated an outstanding charity by two magazines, Sesame Street Parents and Money Magazine.

''As long as there is still one missing child, Child Find Mission is not completed,'' says Ms. Markfield.

Child Find was established in 1980 by the mother of a missing child, and, to date, has helped locate or return through mediation, over 2,700 children.

For further information, or for assistance from Child Find, call 1 800-I-AM-LOST or 1-800-WAY-OUT.