Up there on the bridge of the destroyer you don't really know how deep the submarine is. Your digital electronic instruments are reading out his speed and heading, and you know your position on the chart. But it's not until you hit the switch and - WHISSS - a depth charge goes sailing overboard, that you get some idea of his depth. If you miss, he can get an exact fix on you and fire back and - POW - you're sunk.

Just the routine problems of combat? Exactly right: routine. If you think you can handle more, then turn the switch on Parker Brothers' Code Name Sector to "evasive sub" position - and look out, skipper.

What makes the evasive sub so evasive is a tiny electronic chip, about one quarter inch square, that the people at Parker Brothers call the $40 game's "hidden intelligence." It's actually a miniature computer or microprocessor - a sophisticated descendant of units in pocket calculators and digital watches.

American toy manufacturers are betting heavily that these little computers will add up big profits this holiday season. Controlled by microprocessors, millions of anti-ballistic missiles will be deployed, half-backs on end runs will be tackled and cars will crash into guard rails under the nation's Christmas trees.

"Electronic games are going to be very strong this season," says Wilfred Damisch, merchandise vice president at New York's F. A. O. Schwarz, perhaps the epitome of toy fairylands. "They've become part of the future in the present."

George Ditomassi, whose Milton Bradley Co. is just introducing Comp IV and Electronic Battleship, goes even further:

"We've created more of a stir with these two games than with anything we've introduced in our 117 years."

While calculators made checkbook balancing humanly possible and digital watches made it necessary to have two hands to tell time, this new generation of integrated circuits is poised to hurl curve balls at American kids. No more stacking the Go Fish deck. No more slipping two $1,000s out from your opponent's Monopoly bankroll. The little brains know all. They are so smart, in fact, that they have to be programmed NOT to win all the time.

"You can't always have the computer win," says Jeff Rochlis of Mattel, Inc., which will market electronic auto-race, football and missile-attack games this fall, all in the $25-price vicinity. "It wouldn't be fun if you never beat it. You have to have a feeling of accomplishment at the end.So you program the chip so that you can beat it often enough."

At Hollywood Toys, the largest shop in Los Angeles, there are actually lines of people waiting to buy the Mattel Electronic Football game, which sells there for $39.95.

"Such a toy I've never seen," says owner Leo Gitklig, who left New York 22 years ago to open his West Coast business. "We have calls from all over the state asking for this. The distributor is rationing them out. We were lucky: we bought lots early. I'm worried we won't have any for the big holiday season."

The demand is easily understood once the game is played. A bit larger than a pocket calculator, it has little red blips to represent the players on a green field. It takes some clever strategies to outwit the computer defense. After each play a scoreboard reads out the downs and yards to go; a digital clock times each quarter; the machine blows a whistle after each play and at the end of each quarter. Another display shows the position of the ball on the field.

All of the Mattel games are self-contained, portable and battery-operated. They also contain an electronic sound synthesizer so that when an enemy missile, for instance, destroys your town, the computer plays "Taps." Similarly, when your team scores a touchdown, the computer trumpets "Charge."

"The first generation of electronic games (the pong games that have to be linked with a television) relied on the electronics to provide refereeing and score-keeping functions," says Rochlis. "They could have been created with motors and lights. The game playing is not materially affected by electronics. In this second generation, the computer is really your opponent. It reacts to you and assumes quasi-human qualities."

One quality lacked by the chip, and many of the technicians working with it, is imagination.

"The real problem is one of imagination catching up with technology," says Parker Brothers' Ed Radding. "The limits of what these things can do are almost unbounded. It's a question of figuring out how to take the qualities of the chip and translate them into game functions."

Chips are essentially processing units, combining a memory device with input/output circuitry. Invented in 1958 by Jack Kibly at Texas Intruments, they were originally designed to replace more bulky transistor complexes in military equipment, and eventually became the building blocks of giant computers. They've been a billion-dollar business for the past 10 years. Last year almost a billion chips were manufactured in the United States.

For electronic games, rules and moves and a display mode are programmed into the chip in binary logic: A complex chain of yes or no possibilities. With each move a player makes, the microprocessor analyses the change, decides its next move and then shows that move on a display screen - usually a series of moving dots or a numeric readout.

"The program is written in normal computer language, converted to a deck of punched cards and then converted to a photomask," says Texas Instruments' Dean Toombs. "Then you can just print them photographically. The program which executes the particular game is stored in ones and zeros. The chip takes that stored data and converts it into an output that results in a display."

Most manufacturers refuse to discuss expected sales figures, but Milton Bradley's Ditomassi is "geared up to sell 300,000 Comp IVs this Christmas."

Comp IV looks like a large, handheld calculator. It contains a chip programmed with over 32,000 five-digit numbers. The goal of the game is to punch in digits and guess the number that the computer has singled out. The chip tells the player if he's put a correct digit in the wrong sequence.

"It's like eating peanuts," says Ditomassi. "Very addictive. We chained them to several bars in New York and when I went back a week later people were lined up."

"The thing is like a basic course in logic," says F. A. O. Schwarz's Damisch. "It trains your mind to solve problems in the least number of moves."

"Any company that doesn't pay attention to these games is sticking its head in the sand," says Ditomassi. "A sale of a $30 item is going to take away from the sale of some other item to a certain extent. I mean there's only so much disposable income."

Unlike the Pong games of the last two years, the new generation of games does not require a television screen for display. While they are much less sophisticated in their visual quality, they are also considerably cheaper than the average $100 unit that is connected to a TV. Still, those games accounted for about $40 million in retail sales last year, and the self-contained game manufacturers are looking for an access to that market soon.

"Basically these things are forc-runners of the home computer," says Mattel's Rochlis. "There's a logical transition involved. One way to get into the home-computer market is to sell games. Game play is one set of software. We'll see home systems in but also store financial records, run five years that not only play games, the home security system and turn the appliances on and off."