IN 1891, F.A. Thompson proposed the ultimate mousetrap. It consisted of a piece of wood leading to a bucket of water.

"The rat is supposed to run up along the plank until it comes to the head and, thinking it is rigidly secured, will put its paw out on the nail or pin to get the bait on the hook (at the end of the plank), thereby revolving the said head and causing the rat to lose its balance and fall into the liquid beneath and drown."

Thompson's description of the device is today enshrined in the files of the U.S. Patent and Trademarks Office in Alexandria -- along with a thousand other landmarks of man's eternal search for the better mousetrap.

Thompson's is one of the simplest. Others employed all the guile of the super sleuth.

One design, for instance, proposed to tempt Sampson Mouse with a latter day Delilah Mouse. She was a phony -- a vamp -- equipped with two tiny spears spring-loaded through the tail. He was supposed to nuzzle his shy companion, setting off the spring, which shot the two spears through the eyes.

Oh, the travails of love. He had his whiskers clipped quite handily.

One of the earliest patents dates to March 25, 1856. The device was invented by S. Beaumont. Upon what observations Beaumont designed his trap one can only imagine. It is loaded with springs, strings, levers and rods. The best of the country's engineering heritage was brought to bear.

But it -- and countless others -- was never good enough. New patents followed - and have continued to trickle into the patent office at a steady rate up to the present. various improvements on the

Various improvements on the mousetrap have employed: falling cages; spring-loaded lids; magnetically activated lids; crushing weights; sides that spring up to form a cage; doors than can be pushed open but close to block exit; gravity, to reset the trap automatically; trap doors; falling floors; strings and pulleys that lower the varmint into escape-proof compartments; spring-loaded arms that catapult the rat against the wall; hooks to impale him in the belly.

In March of 1923, Johann Berenyi of Perth Amboy, N.J., coolly explained the merits of his design:

"To enable the animal to be killed in the trap, I provide a vertical plate extending longitudinally in the cage and slidably guided for transverse movement on crossbars extending between the side walls of the cage, this plate having a series of spurs suitably spaced over its inner face.

"The trapper, upon finding an animal in the trap may then release the latch, the springs throwing the plate across the trap and causing the animal to be crushed."

Nice going, Johann.

But there were other, more desperate attempts. Several designs invited Mickey to dine at gunpoint. Many used a wire noose to fit the neck. The advent of electricity caused a revolution in the rat execution trade.

Rube Goldberg has never had much new to say about the mousetrap.

It is easy to lump rats together with mice. But Mickey would be appalled. Rats, such as the Norwegian rat (Rattus norvegicus) common to this area, are much larger than mice and have different habits altogether. For one, they do not appear much in cartoons.

Professional exterminators say mice are more difficult to get rid of for a couple of reasons. First of all, mice do not like to go very far from home -36 inches is their normal range, says. Wayne Scott, president of Crest Pest Control in Kensington. The mouse is content to get his water from the food he eats.Unlike the rat, he will not go long distances in search of it.

So many more traps must be set for a mouse as for a rat, if you don't know where Mickey is hiding out.

Also, "mice are nibblers," says William Roll, the president of American Disinfectant in Washington. If you put out poison for him, "it seems like it takes him forever and a day before he eats enough to kill him. Whereas a rat will sit down tonight or tomorrow night and eat a good slug."

Professional exterminators choose poisons over traps, for the most part, because traps have to be emptied and that means a return trip. Poisons, such as red squill, a plant derivative from the lily family, work well on these rodents because rats and mice never learned how to regurgitate. But red squill, authorities say, is little used now in favor of anticoagulants that cause hemorrhaging.

"People call up here and want us to use something that will drive the rats out. They don't want 'em to die in the house," Roll says. But they will come back, as long as there's food and shelter.

The best idea, it seems, is to have a few traps around for Mickey and some poison for Mr. Rat.

A mouse trap at Hechinger Co. costs $1; a rat trap $1.69. A compound called Mouse Pruff goes for $1.29 in the 4-oz. size; 79 cents for two ounces. Vacor Rat Killer is $2.99 for 13 ounces.

There has been much professional discussion about what mice might best like to find on a trap. Current consensus is peanut butter (crunchy style, naturally). "Some people favor it," says Gordon Christensen, a sanitarian in Arlington County's environmental health department, "because you (the mouse) can't run away with it."

But you may have a trendy mouse on your hands who'd prefer a good slice of Brie. Meat-eating mice go for salami. You just have to try several things until you've mapped out his druthers.

Eugene Gauthreaux at the Terminex company in Hyattsville says the last couple of years have seen a marked increase in mouse infestations. Presently he has about 6,000 accounts, which receive monthly service.

Costs for such service are $16 a month. "We recommend monthly service because ther's no way you can go in one time and get rid of 'em," says Gauthreaux.

One-time jobs can cost anywhere from $25- $100 or more, depending on the extent of the problem.

If the problem is not on your premises, but in the public domain, you can call the city, or county, to deal with it.

"Usually if there is one complaint on the block, the whole area is infested," says Bailus Walker, the director of environmental health services in the District. "We require property owners to clean up their property. If it's on city property, we clean up. We bait the area once, then come back and bait again three weeks later. That usually gives us a 92 percent kill rate."

But the best way by far to handle rodents, officials say, is to eliminate the food supply and entrance. "Rats will not hang around if there's not adequate food and adequate harborage."

If there's a rat problem on your block, you can call for help at: 724-4266 in the District; 468-4087 in Montgomery County; 794-6800 in Prince George's; 750-6251 in Alexandria; 558-2661 in Arlington; 451-7783 in Fairfax.

If it's an apartment you live in, the landlord is responsible for pest control. But it can't hurt to keep a few traps around. You never know who's going to drop in.