IN TWO SUCCESSIVE days last week, two persons were struck and killed by trains in Prince George's County. An elderly woman, trying to make certain that her 7-year-old grandson stayed out of an Amtrak train's path at a pedestrian crossing in Seabrook, was struck by a train traveling at more than 100 miles per hour. An unidentified man who may have been deaf or otherwise disabled never stepped out of the path of a Chessie System passenger train, which could not stop in time.

Maryland officials say they have spent $8.8 million in adding or replacing warning devices at railroad crossings since 1976. But in Maryland and around the nation, the kinds of signs, warning lights and gates that mark some railroad crossings have changed little since the 1930s. In that same time, rail companies such as Amtrak, competing with airlines and buses, have poured funds into better tracks and trains that are faster and quieter -- which means that people crossing the tracks might not hear them until it's too late. The technology of warning, the efforts of education, people's habits and law enforcement have not kept pace.

A train traveling 100 miles per hour takes just two seconds to cover 100 yards -- the length of a football field. Even a "light" train needs two miles to come to a full stop. Heavier freight trains, while slower, take even longer to stop. Railroad officials say too many people think trains can stop as easily as automobiles. Citizens complain that too few crossings carry signs that clearly state the dangers. Both say police departments can do a service by ticketing those who ignore safe railroad crossing procedures.

A federal program known as "Operation Lifesaver" has been in progress for the past year. It is designed to educate everyone from children to truckdrivers about the dangers of trespassing on railroad crossings. Federal funds are being used for research to develop new railroad crossing warnings that might be safer and easier to understand.

There were only eight instances in which pedestrians were struck by trains in Maryland in 1984. Some of those were found to have involved suicidal people. But as trains get swifter and quieter and, therefore, become harder and harder for children and the elderly especially to judge, it is reasonable to ask that warning devices become more effective as well. Even at current speeds, these trains are very safe when compared with automobiles. If warnings and signals cannot do the job, however, then it may become necessary to apply to main railroad routes the kinds of safety requirements -- chain-link fences, barriers and grade separation crossings -- routinely used for major highways.