Five years ago today, Sheila Lyon, 12 and her sister, Katherine, 10, walked from their suburban home in Kensington to the Wheaton Plaza Shopping Center. They have not been seen since.

Sgt. Rodney Ingels of the Montgomery County police department, the investigator most familiar with the baffling case, said in an interview that "except for a helluva lot of work, we're no further than we were" when the investigation began on March 25, 1975.

The Lyon sisters -- the mere mention of those words gives chills to many parents to this day -- left their home on Plyers Mill Road about 11 a.m. that Tuesday. They had less than $4 with them. Their mother, Mary, said she expected the girls to return home by 4 p.m.

About 2 p.m., their brother, Jay, 5, saw them munching pizza at the Orange Bowl, a popular teenage hangout in the sprawling shopping center, which was packed that day with children enjoying their spring vacation from the Montgomery County schools.

"That's the last spot I can place them," Sgt. Ingels said. "From that point, there is absolutely no evidence. Not a single suspect, and no motive." p

Ingels, who was assigned to the case the day after the girls disappeared, has spent more than half his working time since checking out thousands of leads and tips provided by classmates, neighbors, family friends, private detectives, scores of psychics and hundreds of strangers who have read about the case.

Aside from the fate of the girls, the most frequently asked question is about the rest of the family. How have the parents, John and Mary Lyon, and their other children, sons Jay, now 20, and Joe, 14, managed to carry on amidst the uncertainty?

John Lyon, a radio station announcer and disc jockey, said the other day that "everybody's fine . . . the boys are great." Understandably, he's not anxious to "bring it all up again," but he said he realized the five-year anniversary inevitably would bring press inquiries.

"We're ready for the crap," Lyon said in the same mellow, relaxed voice that masked his trauma in the weeks following the disappearances, when listeners to WMAL marveled at his ability to spin records and banter about the weather.

Interpreting Lyon's professional calm as a lack of concern, "some people tried to cast suspicion" in the father's direction, Sgt, Ingels said. "The family is aware that we did a complete blackground check on them. There is not an iota of evidence that anything occured in that house."

Ingels said the family "doesn't believe this case needs publicity," but the stories persist.Last May, the National Enquirer ran a story under the headline, "Baffled Police Ask Enquirer Readers: Help Us Find Two Missing Girls."

As a result, Montgomery County police recieved more 100 tips," "Most of them from psychics, who sent tapes and maps from as far away as Puerto Rico and Hawaii," Ingels said.

One woman sent a St. Christopher medal to Ingels, saying she was praying for him to find the girls.

"We collated the latest reports with earlier ones," said Ingels, who treats every tip as if it were the one that could solve the mystery. "But there was no real pattern. About 90 percent of the psychics think the girls are dead. They send maps pinpointing where the bodies can be found, but often they don't identify the state," he said.

Ingels said "the average citizen who has followed the case thinks the girls are not alive, and the odds are that they are not. But I can't afford the luxury of having a theory. I have to maintain an open mind."

The detective ticked off the various theories and what he knows about them:

KIDNAPING -- "In 99 cases of 100, they ask for a ranson, and we haven't had that." Shortly after the disappearance, there were a number of amateurish extortion attempts, including one in which Lyon deposited $10,000 in a bus station locker in Annapolis, as a caller had ordered. No one claimed the money.

WHITE SLAVERY -- Although kidnaping for the purpose of forcing them into prostitution would not result in a ranson call, "they were a little too young for that purpose."

SEX OFFENDER -- "Because there are two of them, it would be difficult to hold both of them this long."

(The return last month of a 14-year-old California boy, abducted seven years earlier, sparked a flurry of calls to Montgomery police asking if the California kidnapper might be connected to the Lyon sisters. No such connection could be found.)

RUNAWAY -- "There was no turmoil in the family, no reason to run away." Also, the girls are now old enough -- Katherine would be 16 this coming Saturday and Shelia 18 on Sunday -- that they could return and insist on living on their own.

HOMICIDE -- "Usually results from one of three factors -- family trouble, underworld activities or gambling -- all missing here."

Ingels said he has learned in this five-year investigation that although "there has never been anything like this in Montgomery County, or anywhere in the Washington area," children disappearing without a trace are not uncommon in places such as New York, Chicago and Los Angeles.

He noted that in the case of John Wayne Gacy Jr., the Chicago man convicted of the sex killings of 33 young men and boys, "about one-third of the victims were never reported missing by their families."

Ingels also believes that if the girls' bodies had been buried, "their remains would have turned up by now. Animals do a good job of digging. But there are other ways of disposing of bodies, like in the Gacy case," in which 26 of 33 victims were buried in the crawl space of his home.

Ingels, a 40-year-old investigator with 20 years of experience on the force, hoped that he would be on the case "until it was solved or I retired.'" He is eligible to retire in five years. But on Feb. 3, he was promoted to shift supervisor, and was forced to turn over the files to another detective.

"A fresh view is good for every investigation," Ingels acknowledged, "but I know this case like the back of my hand. If there were a way to hang on to it, I would."

Over the years, Ingels has established a rapport with the Lyons, whom he calls "an average American family." He has observed their attitude change, and knows "exactly how they feel today." Although he won't betray their confidence, Ingels said the family "is very much in tune with reality."

Henry and Winnifred Alberding, whose backyard adjoins the Lyons', see John and Mary Lyons almost daily. They exchange greetings across the chain-link fence, but never talk about the girls.

"There's nothing to discuss," said Alberding.

The Alberding's daughter, Gina, 18, is nine months older than Sheila Lyon. The girls used to take turns spending weekend nights at each other's house, "depending on who had the best thing to eat that night," said Gina, who finds it "amazing" that "Sheila will be 18 this week," always speaking of her friend in the present tense.

Gina doesn't believe the Lyons are "resigned" to the outcome. "They could never give up hope," said Gina, adding, "If only they knew, one way or the other."

The Lyons have "worked very hard at not being overly protective with the boys," said a friend of the family. Jay attends Montgomery College and Joe is at Einstein High, where Sheila would be a senior.

After staying close to the house for a long time, Mary Lyon enrolled in classes at Montgomery College and "made A's and enjoyed it," but quit to spend more time with her sons.

John Lyon's career "seems to have taken off" lately, a friend said noting that he now is seen in some television commercials in addition to his radio job. He still plays in a blue-grass band, but doen't bring the boys home so often for late night parties. "He's much more quiet now, to himself," observed Alberding.

"You adjust," said one of Mary Lyon's friends. You adjust because you have to when you have other children."