In one of her recent VIP columns, staff writer Maxine Cheshire reported that many of the important participants in the Reagan inaugural festivities will be wearing clothing lined with a light-weight material that is bulletproof.

Apparently Henry the K set the fashion while he was secretary of state and therefore a target for assassination. Later President Ford wore a golf jacket lined with the material, and when Pope John Paul II visited this country, a group of New York policemen chipped in and bought him a protective coat. Several state governors and high federal officials who will be nearby when Ronald Reagan takes the oath have also ordered the bulletproof linings. With so many unstable people carrying handguns these days, public officials are beginning to regard protective clothing as a necessity.

Louise G. Cooley of Bethesda tells me that when she read that column, her mind went back to a story told her by Sister Thecla of the House of the Good Shepherd.

At the time of the story, near the turn of the century, the Good Shepherd order was housed in a convent at 3601 Reservoir Rd. NW (where the Sisters of the Cross are now). Sister Thecla was a novice in the Good Shepherd congregation. It was her custom to say her Office as she walked back and forth on the convent porch.

When the weather permitted, a dashing young man used to ride by on horseback each morning. When he reached the convent he would rein to a stop, rise in his stirrups, and wave his hat to Sister Thecla.

Sister Thecla would wave back, and the lone horseman would then ride off at a gallop.

But after a time, Sister Thecla became worried about the propriety of a young novice waving to a passing horseman.

So she went to the Mother Superior for guidance.

"It's perfectly all right for you to return his greeing," the Mother Superior said. "After all, he is our president, Theodore Roosevelt."

I wonder what Teddy would say if he could see the elaborate security precautions that must be taken now to protect our high officials. I don't have to wonder what the Secret Service would say if horseman Ronald Reagan would express a desire to gallop off without the accompaniment of an adequate bodyguard.

As Louise Cooley says when she relates Sister Thecla's story: "We've come a long way, haven't we baby?" BACKUPS REVISITED

A few days ago, I wrote about the backup power system at Dulles International Airport. When Vepco's line into Dulles failed, the backup power system had also failed.

When he read my comments, Bill Carnes, chairman emeritus of the Airlines Electronic Engineering Committee, was reminded of a story about Lt. Gen. Harold Grant.

Grant is now retired. When he was deputy administrator of the Federal Aviation Administration he was known for his thoroughness.On one inspection trip, for example, he asked about the backup power: "Will it work for sure?"

He was assured that it would, and was invited to pull the master switch and see for himself. So he pulled it -- and for several hours, thereafter, the entire East Coast military communications system was fouled up.

I called Gen. Grant and asked him if he could remember why that backup system had malfunctioned. He said he did. "The backup power came on quite quickly," he explained, "but not instantaneously. That was the problem. The power was off for only a fraction of a second, but that was enough to throw some of our equipment out of synchronization. It took a couple of hours to realign it."

At Dulles the backup power came on but a circuit breaker went out. It's always something, and perfection continues to elude us. MEA CULPA

Carl Burrows asks why last Tuesday's column spelled convalescence "convalescense."

It wasn't my fault, Carl. I looked the word up to make sure that it ends in ce , not se , so don't blame me.

Blame the idiot who operates my video display terminal. He's the one who misinformed the computer.

(Gee, I sure miss the good old days when a fellow could blame something of this kind on a Linotype operator. Now there's no place to hide.)