President Reagan told a story in Florida Wednesday about baby diapers to illustrate his view that courts foolishly adhere to technicalities in allowing some evidence to be thrown out of court if it is obtained illegally. Police in California a few years ago found heroin in the diapers of a baby but the case was thrown out, Reagan said, "because the baby hadn't given its permission to be searched."

The president, a collector of newspaper exotica, has been embarrassed in the past when some of his stories have failed to check out. But the diaper case turns out to be very nearly all true.

They are still talking in Colton, Calif., 60 miles east of Los Angeles, about the Dec. 29, 1969, search of the home of Robert Garcia Cordova and Ramona Padilla, and the packet of heroin found in the diapers worn by Padilla's 9-month-old daughter (Reagan, in a small slip, indicated the child was a boy). Municipal Court Judge Theodore G. Krumm ruled that the baby had not been named in the search warrant and so her diapers had been illegally examined.

Joseph Burns, the San Bernardino deputy district attorney who prosecuted the case, said then, and insisted today, that "the Fourth Amendment which prohibits illegal searches was not designed to protect the rights of a baby."