Letter carriers in southern Montgomery County are initiating a program Friday in which they will keep a watch on the homes of elderly or handicapped residents to help ensure that they are safe and sound.

Between 500 and 1,000 senior citizens and handicapped residents who live alone are expected to participate in the program, called Carrier Alert, according to Denise Ridgely of the Montgomery Red Cross, one of the program's sponsors.

Participants' homes will be marked to signal letter carriers to watch for any accumulation of mail. If the mail has not been picked up or there is some other sign that the resident may be in trouble, the letter carrier will call his supervisor for help. The supervisor will then contact either the Red Cross or police officials.

"This is a highly commendable effort to sensitize the public, and in particular the letter carriers, to the needs of the elderly and handicapped," said Janet Kirshner, director of senior adult department of the Jewish Community Center of Greater Washington.

She described Carrier Alert as a step in the direction of old-fashioned neighborliness. "I think we all should be more aware of our neighbors and look out for their concerns," she said.

The program, which is available in Bethesda, Chevy Chase and Silver Spring, formalizes something many letter carriers already do, according to Fredrick Price Jr., manager of customer services at the Bethesda Post Office.

"Carriers are going out there doing these things now, but we have a lot of carriers who don't know what signs to look for," he said. Now substitute and new carriers will see the marking and know to watch for an accumulation of mail, Price said. The program will also provide a formal process for notifying authorities.

Ridgely said that 2,800 applications for the program have been "Carriers are going out there doing these things now, but we have a lot . . . who don't know what signs to look for."

-- Fredrick Price Jr.

sent to senior citizen centers, post offices and libraries, she said.

Carrier Alert was started by the National Association of Letter Carriers five years ago in Baltimore and New York, Ridgely said.

Even without a formal program in Montgomery County, three elderly residents in trouble have been aided recently by alert letter carriers, Price said.

In May 1985, an elderly woman in Chevy Chase fell and broke her hip. She did not get help until three days later when her letter carrier became worried about newspapers on the porch and called the police, according to Price. The woman was more concerned about her dog not being fed for days than herself, he added.

Another elderly woman spent a day and a half in January 1984 locked in the bathroom of her Bethesda home when a letter carrier noticed that the television had been on for two days while no one appeared to be watching it and the mail had not been picked up, Price said.

Another woman was found unconscious by a letter carrier in May 1985. The carrier noticed the mail was accumulating and contacted a neighbor, who called police.

The program is sponsored by the Postal Service, the National Association of Letter Carriers, the Red Cross, Safeway stores, and the Montgomery County Department of Family Resources. For information, call 588-2515.