WHETHER YOU USE the best day of the week to wallow in newspapers or football games, to rearrange the living room or hoe the garden, the appeal of Sunday is simple: For 24 hours, you don't have to do anything you don't want to.

But sometimes reality intrudes, in the form of a broken-down TV set an hour before kickoff time, or the sudden realization that it's your mother's (or husband's or best friends) birthday and you're without a present. Before panic sets in, be advised that more and more Washington businesses are choosing to stay open on Sundays.

True, supermarkets and drugstores have been doing this for years. But did you know that you can also get your hair done, take your cat to the vet or stock up on stamps on Sunday? And that's not the half of it.

Nothing to read? Try one of the 14 libraries in the area with Sunday hours - or the more than four dozen bookshops. If your eyes get tired, you might want to get them checked right away - at My Sunday Optician, which is open, you guessed it, on Sundays. Or, you could spend your Sunday getting a physical. The doctors at Medic 24, a private family practice group in Baileys. Crossroads, are open all day. If your car breaks down on the way over there, there is someone who will tow it and, even better, repair it on Sundays.

Sunday shopping wasn't always this easy. As little as 20 years ago, ice cream trucks weren't permitted to ding their bells in the District on Sundays. Washington pastors were urging Sunday sales boycotts, and denouncing Sunday shoppers as Communists."I believe that any business that does business on a day of worship where it is not absolutely necessary is contributing to the moral and spiritual breakdown of our country and weakening our position among the nations of the free world," one prominent pastor expounded in the mid-'50s.

He was just following tradition. In colonial Virginia, citizens got three warnings for skipping church. Then they were put to death.

Now life's a little easier for those of us whose schedules don't conform to our forefathers' idealized views. It's easier for the shopkeepers, too.

"Sunday is fun day for us," said Richard Howorth of the Savile Bookshop in Georgetown. "It's a nice slow pace, but at the same time business is remarkably good. And the customers are different from any other day. I don't know if they've just been to church or what, but it's like they act civilized one day of the week. It's just completely different from Saturday."

Of course it all depends on your line of work. The customers encountered by, say, TV repairmen are a little more demanding than book-lovers. "You can always tell when there's a game," said a technician at Associated TV of Virginia. "They turn on their set and nothing happens. They have people over, it's embarrassing. They call us up in a panic."

Associated TV of Washington has found the same thing. "They can get pretty demanding," the manager said of his Sunday customers.

Whatever the incentive, the store owners say, people are taking advantage of their being open. "We're into our third year now, and it's very successful," a Hecht Co. spokesman said. "As people become more familiar with us being open, we see our weekend business getting stronger and stronger - especially on Sundays."

The need is definitely there, says Michael Sattelmaier of My Sunday Optician. "We do more business in the four hours we're open on Sunday than we do during the week. It's one of our busiest days. We get people with emergencies - their lenses break, their frames will break. Or we'll get people with not time during the week, whose only free time is after church on Sunday. And then remember there's no traffic, and parking's easier. I don't know, I should try to analyze these things, but we're too busy. We just open the doors and stand back."

Of course there are drawbacks to all this shopping freedom. "I wouldn't be in here buying this mattress," said a man in Montgomery Ward's last Sunday, "but I felt that since the store was open I had to keep doing the chores I didn't get done on Saturday." There's a reverse Puritan ethic at work here - Sunday used to be the only day you didn't feel guilty for not working.

But for most of us, Sunday shopping means, simply, freedom of choice. Here's just a sampling of some of the services you can choose from.