That's not a picture hook - it's a 'bug'

One hundred eighty miles above the earth there soars an electronic eye so keen that eagles, by comparison, are blind as bats wearing sunglasses. This marvel is the US KH-11 spy satellite, alias ''Keyhole.'' The KH-11's cameras can pick out cars in the Pentagon parking lot - while the satellite is over, say, Detroit. They can see moving tanks in the dark, and are able to detect camouflage trees.

''US satellites are the best in the world,'' says a former military intelligence officer, arms waving with excitement as he discusses the subject. ''Easily the best in the world.''

They are also the cutting edge of a technology most Americans know little about: high-tech surveillance equipment. Over the last five years, microchips and miniaturization have led to tape machines that can record 40 conversations at once, tiny TV cameras that see in starlight, and ''bugs'' disguised as picture hooks.

One firm even predicts that camera-equipped computers will soon be able to recognize individual people.

These devices, for the most part, are intended for good use: catching crooks, plant protection, international intelligence-gathering. In many ways they make our lives more secure.

Yet the very existence of these high-tech eyes and ears compels our vigilance - just in case - say those who study privacy subjects.

''We have all the technology (Orwell) anticipated,'' notes Robert Smith, publisher of Privacy Journal, ''and more.''

In fact, an amazing array of surveillance devices are available off the rack, like ready-to-wear suits. Others can be easily assembled from parts sold at many radio and drug stores.

* The Dictaphone ''Veritrac,'' sold mainly to law-enforcement agencies, is a refrigerator-size tape recorder capable of monitoring 40 phone calls at once. At the other end of the scale, CCS Communications of New York sells (in states where it's legal) a desktop humidor that contains a tiny, voice-activated recorder.

''There are microcassettes (recorders) advertised in the Wall Street Journal that are vastly better than anything the government had five years ago,'' claims an electrical engineer who has worked with intelligence agencies. ''They fit right in your palm. They don't even stick out beyond your fingers.''

* Video cameras the size of a deck of cards will be available this spring from RCA Corporation. In place of bulky image tubes, these tiny eyes use slices of photosensitive silicon. Cameras currently on the market can already ''see'' by starlight and transmit pictures by microwave.

* Motion sensors that use infrared or ultrasonic waves, once limited to space shots and expensive weapons, have become standard items in the catalogs of such security firms as ADT and Racal. They are used in spots where normal cameras are useless: The National Park Service, for instance, has used infrared sensors in the recent past to count hikers in heavy forest foliage.

* Advanced technology has rendered the ''bug'' planted by the Watergate burglars as obsolete as a phone made from tin cans and string. Mix together the microphone from a hearing aid, a pared-down watch battery, and a few odds and ends, and you can today produce an illegal listening device the size of a picture hook.

''They only work a few hours or days, but you can't even recognize them as bugs,'' says Harry Augenblick, head of Microlab/FXR, a company that makes bug detection devices.

Furthermore, surveillance gadgets today are often linked together in security systems, then turbocharged with add-on electronics. This extra power gives the systems a smattering of ''intelligence.'' RCA's digital motion detector, for instance, enables cameras to distinguish between a guard on routine rounds and someone entering a restricted area.

Advances in computer technology will eventually make security systems even more discerning.

''Now there are special computers being designed that will be able to recognize people,'' says Harold Krall, an RCA vice-president of the closed circuit video equipment division. ''This whole industry is in tremendous ferment.''

Of course, equipment sold at the corner security store is crude and bulky compared with the high-tech eyes and ears used by the United States government. ''Q,'' the disheveled gadgeteer who makes James Bond's espionage knicknacks, has little imagination compared with the scientists who work for the Pentagon.

US intelligence agencies, for instance, have in the past trained pigeons to deposit bugs on windowsills, according to congressional documents. They have experimented with microwave lie detectors that measure stomach flutters from half a mile away. Eavesdropping lasers, which work by ''listening'' to windowpane vibrations, are reportedly standard Central Intelligence Agency (CIA) fare.

But the Mercedes of surveillance devices is undoubtedly the US spy satellite. The most advanced US skyborne eye, the KH-11, orbits the earth at an altitude of 160 to 180 miles, snapping away with both enhanced-color and infrared cameras, according to intelligence and scientific sources. Photos are either beamed straight back to earth or dropped overboard in parachute capsules.

Its multicamera capability allows the Keyhole to see in the dark and strip away camouflage. The satellite can focus on objects as small as a Toyota - but it can't yet pick out lettering on crates, or tell Cuban advisers from Nicaraguans.

''A lot of the stuff you hear (about the KH-11), reading license plates and things like that, is exaggerated,'' says one knowledgeable source.

Other surreptitious US satellites include the KH-9, which scuds along in a low orbit for clearer pictures, and the Rhyolite, which eavesdrops on radio transmissions from its parking spot 22,000 miles above the Earth.

The purpose of all this electronic gear is to spy on foreign nations, so the US can know better what's going on in the world. There is evidence, however, that these satellites have in the past turned and focused on Americans.

A CIA memo of May 8, 1973, written by then-Deputy Director Edward Proctor, implies that the US government spied on domestic demonstrations from space. The memo, obtained by the Center for National Security Studies and read by this reporter, says that the agency's satellite photo arm ''has examined domestic coverage for special purposes such as natural catastrophes and civil disturbances.''

In addition, Dow Chemical in 1980 accused the US of using satellite photos to monitor pollution from factories.

This sort of evidence leads to the larger issue of control of surveillance technologies. Should we worry about the advent of 40-track tape recorders and fist-size TV cameras? Once computers have been trained to recognize people, will they someday be programmed to search for us?

The advent of computerized information networks - automatic teller systems, electronic mail - makes this question of control of technology more urgent.

''Technology can create new opportunities for privacy invasion, manipulation, and control,'' concludes an Academy of Political Science privacy paper, ''but it does not by itself create the structure of power that commits those abuses.''

Notes Anthony Oettinger, head of the Harvard Center for Information Policy Research: ''The problem with the metaphor of Big Brother is that it suggests some kind of outrageous dictatorial power (is out there). Reality is much more subtle than that.''

Next: electronic eavesdropping.