Nazek Fahmy was frustrated. Like thousands of other Washingtonians, she had combed the newspapers in search of post-Christmas bargains, and then headed out to Montgomery Mall yesterday. But the bargains were proving to be elusive.

"It's so hectic and crowded," Fahmy complained. "It's worse than the Christmas rush. I've been here for hours, and I haven't been able to buy a thing."

"Not only was it difficult to get waited on, she said, pointing to the long lines around her, but she was having a hard time finding what she wanted.

A graduate student from Egypt now at the University of Maryland, Fahmy was rushing into Sears to try to find a few things while her husband watched their two young daughters in the mall. "Everyone told me to wait to buy things till after Christmas," she said, "so I did. But I don't know whether it's worth it at all."

Those returning merchandise, as well as shoppers, found their best-laid plans going awry yesterday.

At Tysons Corner Center, members of the post-Christmas throng were overheard voicing their displeasure with ill-fitting boots, confusing pasta makers, sweaters that clashed, and relatives with no taste. But the bitterest invectives by far were reserved for a small white sign posted at the entrance to Bloomingdale's:

"Closed Monday for the Holiday."

Many would-be patrons carried Bloomingdale's bags and boxes as they bounded eagerly up to the door, grasped the handle, pulled, and finally came to the realization that they were dealing with an immovable object.

"Ay, ay, ay!" said one forlorn woman upon deciphering the sign at the west entrance. "So much for Bloomingdale's!" she exclaimed to her husband.She had come, she said, to "return something that was too large in lingerie."

The voi ce of a jeans-clad teen-ager oozed with sarcasm as she told a companion, "Bloomingdale's is too good to be open!" She hadn't bothered to telephone or check the newspapers. "You just assume they'll be open the day after Christmas," she explained.

"I purposely parked near Bloomingdale's to avoid the cold," said a shivering young woman. She had sensed that something might be amiss, when she had sighted the small crowd gathered outside in apparent confusion.

Virtually all of Tysons Corner Center's 135 other stores were operating as usual yesterday, and at most of them business seemed to be brisk.

Britches Great Outdoors at Montgomery Mall was as mebbed as any of the other stores offering sales - but Britches wasn't having a sale.

"People are going crazy," said saleswoman Niki Albert. "They expect us to have a sale, and we're not. But they are buying anyway. They come in and practically rip things off the shelves.

"And exchanges, exchanges! The line was stretching all the way back a little while ago."

George and Pat Morse, a Bethesda couple, purchased a dinette set on sale at Sears. "We didn't get the one we'd planned to buy." said Mrs. Morse."The one we got was much more expensive. We'd have had to wait six to eight weeks for delivery for the one that was advertised, so we decided to look at something else. And we found a set we really liked, but it cost a couple of hundred dollars more. I guess that happens a lot."

Just because it was a day of big sales didn't mean one had to miss the day's other big attraction - football. The men and young boys gathered in front of the rows of television sets in Seats at Montgomery Mall watching the Dalls-Chicago game were clearly making the best of an imperfect situation.

The crowed ebbed and flowed, somtimes blocking the escalator nearby. This caused an unhappy sales clerk to rush out and ask people to move to the side. They did, for a few minutes at least, but after a while their numbers grew, and once again they blocked the escalator. The clerk apparently knew when he was beaten: he didn't show his face this time.

The young woman wearing a Hecht's sales clerk pin on her sweater was rushing through the crowds at the Montgomery Mall Sears.

What was life like in a department store the day after Christmas?

"It has been hell," she fairly shouted. "Everybody's returning things, everybody's buying things, and I'm going crazey. You should see the lines in my department (men's and boy's clothing)."

But what was she doing now?

Sheepishly: "Shopping on my lunch hour, I know - it's unbelievable. But there are such good sales."

The return line in the men's department at Hecht's Montgomery Mall store was perhaps a dozen deep in people - mostly men - with Hecht boxes under their arms.

Al Palms, a Rockville management executive, was on of them, returning a shirt that didn't fit. He wasn't planning on searching out any sales merchandise, he said, because "I hate shopping. I'd rather wait till everyone else is done."

But then there's nothing left, someone reminded him.

"That's right," he laughed. "And that way I don't spend too much money."

The costume jewelry glinted around them as women jostled each other in their haste to get at the riches: Woodie's half-price jewelry sales was on, and the shoppers at the downtown store were not deterred by having to reach over purses, shopping bags, and other eager arms to find the booty they were after.

Barbara Guyon, a statistician for a Washington accounting firm, was one of those successful in her quest. One hand grasped half a dozen pairs of earrings, while the other hand tried to get a sales clerk's attention. "I like to buy whatever there are good sales on," she explained, " and this is a good sales."

George Stohmer was having a little trouble with his balancing act - carrying five boxes of Christmas cards and four boxes or (ornaments piled on top of one another, and trying to keep the column intact. He did not totally succeed.

He was enjoying himself, though, he said, as he joined dozens of other shoppers at Woodies' half-price sale of Christmas cards and ornaments. "I like to see the downtown area being used," explained Stohner, a lawyer who lives on Capitol Hill.

Rose Stabe and Laverne Allen, retired government workers, were also buying a goodly number of cards at Woodies's downtown, something they do every year after Christmas. "We buy 100 cards," explained a smiling Stabe, "becaues we have 100 friends." CAPTION:

Picture 1, A woman, looks over winter coats on sale at Sears at Montgomery Mall.; Picture 2, Marked-down coats await bargain-hunters on a Sears rack and,; Picture 3, Die-hard football fans makes use of Sears' television demonstrators to watch the Dallas Cowboys beat the Chicago Bears.