In the lost and found department:

LOST (but later found, under hilarious circumstances): one 23-year-old legal secretary from Arlington named Mary Lettrich.

While waiting for a ride home at 18th and L streets NW one night, Mary decided to duck into Latt's Country Squire, a clothing store, to try on a few things.

It was shortly before 6 p.m., but Mary thought nothing of it. She found a dress she liked. The saleslady showed her to the dressing room. Mary was half into the outfit when . . .

Sudden blackness.

That's right. The sales staff had turned off the lights and locked up, forgetting their potential customer.

Groping through the darkness of the store, Mary managed to find the lights. All the while, she said, "I was thinking to myself, 'This only happens on television.'"

Her first move: try the locked front door. That brought the steady buzz of a burglar alarm. Which brought a phone call from the burglar alarm company. Mary answered.

"You work there?" asked the alarm company man.

"No," said Mary, "I'm a customer."

"You're a customer?"

"I don't believe it either," Mary said.

By this time, police had arrived, but they couldn't get in, either. Nor could the alarm company find the owner, who had the only key.

So Mary was good and stuck. She called her boy friend, Phil Poletti, to tell him she'd be late for their date. Once he stopped laughing, he drove downtown--with a camera. That's when things got truly lively.

For the next two hours, as the alarm company continued to search for the owner and as Phil snapped photos, Mary turned model.

"Hats, dresses, you name it" is what she tried on--and showed off in the front window. Passersby stopped and stared. Mary finally quit and donned a bathrobe. "I figured if I was going to be there all night, I might as well be comfortable," she said.

After nearly 2 1/2 hours, though, the owner was located. He called. Again, Mary answered.

"I've been in business for 40 years and this has never happened to me," he said.

"I've been shopping for 23 years and this has never happened to me, either," replied Mary.

He agreed to come downtown and let her out. But shortly after he hung up, Mary discovered a drawerful of keys by the cash register. She fished out one "that looked right"--and it was. Phil kissed her, the cops shook their heads and the siege of a summer evening was over.

LOST (and later found, much against the odds): $120 in cash.

Pete Duey of Falls Church inadvertently dropped that sum on the floor of Clyde's pub in Georgetown. Busboy Kevin Close found it. He turned it over to nightside manager Jack Trenta. Meanwhile, Pete discovered his loss the next morning and called dayside manager Wendy Burgess.

"I know it's about a thousand to one . . . ," he began.

But the long shot had already come in. Jack had already alerted Wendy. That night, man and money were reunited.

FOUND (under curiously coincidental circumstances): a pair of glasses.

Mike DiFonzo works for a company that makes loans. Mike's job is to chase deadbeats who don't make payments. He is a specialist in finding people who are hard to find. As a result, he looked on it as a challenge when he found a pair of glasses in the middle of the street at New York and New Jersey avenues NW.

The glasses were inside a case, which bore the name Mike Toscano and an address in Northeast but no phone number. DiFonzo began calling neighbors. He reached one who knew Toscano, and who agreed to take a message to his house.

When Toscano called DiFonzo, he was appropriately grateful. And where could he pick up his glasses?

"Well," said DiFonzo, "I work at 400 First St. NW."

"Hey," said Toscano, "so do I." A couple of floors above, as it turned out.

Never has DiFonzo had to travel so short a distance to find his man.