John Walsh believes that many state legislatures are "negligent."

In a voice hoarse from urging state legislatures to pass stronger child- protection laws, Walsh, whose 6-year- old son was abducted and beheaded, says he is frustrated over those who put politics ahead of youngsters.

"A child could be taken across a state line and buried in an unmarked grave and you'd never know it," he says, because only five states -- Iowa, New Jersey, Kentucky, Florida and Connecticut -- require that their missing children be listed with the National Crime Information Center.

On Monday night, for the third time, NBC will air "Adam," the tragic story of Walsh's son, ending with what has become a sad tradition -- a roll-call of missing children. This time, President Reagan will add an appeal to viewers. And this time, the new National Center for Missing and Exploited Children is ready: its hotline (800/843-5678; Washington number: 634-9836) has been expanded from seven to 40 lines and its 30 paid staffers will be augmented by volunteers.

Between Oct. 19, when the hotline was installed, and March 31, the center tallied 21,890 calls. Of those, 2,096 were reports of sightings of missing children and assisted in the recovery of 841 youngsters. (The center, founded and funded by Congress, routes the information to appropriate law enforcement agencies, but does not search for the children.)

During the 51/2-month period, 1,761 calls concerned parental kidnappings of children, 1,216 concerned runaways, 95 involved abductions, 131 involved missing persons over 18, another 191 reported sexual exploitation of children, and the remainder sought information.

The center -- at 1835 K St. NW -- staffs its hotline around the clock seven days a week, except from 3 a.m. to 9 a.m. (on Fridays, from 3 a.m. to 7 a.m.) when callers are asked to leave tape- recorded messages.

Walsh, a consultant to the center, has traveled almost continuously this year to urge the passage of stronger child-protection laws by state legislatures. But the passage of child- protection laws is an issue without much funding, he says, and even it can become embroiled in politics. Walsh said the Illinois legislature failed to pass a law requiring background checks for teachers because "the teachers' union opposed it." And he told of one legislator in a southern state who blocked passage of child-protection legislation because his political rival had introduced the bill.

But there's good news as well for a tired and frustrated and driven John Walsh. In December, his wife Reve gave birth to a son, Callahan, at Fairfax Hospital ("I haven't seen Callahan in 40 days," Walsh admitted in a call from Minneapolis, where he waited to make yet another speech.) Their daughter, Meghan, born after the death of Adam, is 21/2. The family lives in Oakton, Va., but Walsh hopes to return to Florida in a year or so to resume his career and a more normal family life.