A young Briton who had the technological skill to plan an enormous computer theft but lacked the streetwise know-how to carry it off ended his brief criminal career last night in an old-fashioned cops-and-robbers scuffle on a London street.

Despite its failutre, the caper gives large corporations something to worry about and points up the potential for ambitious criminals to score in a fledging field - computer crime.

Rodney Cox, 25, and an accomplice were arrested by London police after Cox demanded nearly half a million dollars from a big multinational company in return for stolen computer tapes.

Despite its failure, Cox's computer caper gives large corporations and ambitious criminals, something to think about.

Cox had been in charge of one shift at ICI's data processing center in Rozenburg, the Netherlands. ICI, which used to be called Imperial Chemical Industries until its public relations department decided on a more modest, profile, is Britain's biggest industrial concern with sales of $5.3 billion in 1975.

Cox had been passed over for promotion and openly grumbled about his fate. Then his boss, Geoffrey Cowlin, had to tell him the bad news. As of Feb. 1, Cox was fired.

The computer programmer decided to arrange his own severance pay. Last Saturday, he drove from his Dutch home to the Rozenburg center and helped himself to about 1,000 pounds of computer tape wrapped on discs. [WORD ILLEGIBLE] .

Security guards, accustomed to seeing the data processing men work at all hours, helped Cox load the tapes into his station wagon. He drove off, according to the police, with all the future financial plans of ICI in Europe worth a mint to any rival chemical company.

Cox then stopped at ICI's European headquarters in Rotterdam to pick up a duplicate set of tapes, a back-up in case of fire.

Just to recompile the millions of bits of information and restore them would cost ICI weeks and nearly $200,000.

The chief value of the tapes, however, lay in the possibilities for a competitor. Large corporations make detailed plans five years ahead for capital investment, sales targets, new products, research and development and this, is what Cox held, police say.

On Sunday, Cox called his boss Cowlin, told him what he had and demanded about $400,000.

At this point, Cox apparently intended to ransom the tapes in the Netherlands. But now he was out of his element. He called Cowlin again and told him to go to ICI's London headquarters and wait for further instructions.

Cowlin conferred with his bosses and they called the Dutch police, who got in touch with Interpol and Scotland Yard and a trap was set for the computer crook.

Monday night, Cowlin arrived in London to be briefed by Yard detectives. On Tuesday, he was at ICI's skyscraper headquarters on the Thames River, waiting for Cox's call.

Cox, according to police, had brought his brother-in-law, Rhys Jenkins, 26, in on the scheme, but neither knew quite what to do next.

Cowlin was told by police to demand proof that Cox actually had the tapes. Cox bit on that.

At noon yesterday, a taxi delivered a package to Cowlin containing two of the missing spools.

At dusk, another taxi arrived. This time, the handover was to take place, and Cowlin was equipped with a suitcase. It supposedly contained the ransom money in old 10-pound notes.

The cab driver handed Cowlin a letter instructing them where to go next. Cowlin, armed with a small police radio, told the unmarked cars following him to head for Oxford Street.

There, at the height of the evening shopping hour, Cowlin got out of the cab by the Lord John Boutique. He stood with the suitcase in his outstretched arm for three or four minutes.

At last a motor scooter drove up with two young men abroad. One lunged for Cowlin's suitcase. A dozen detectives, some dressed as street cleaners, piled on the pair and wrestled them to the ground.

Soon, in the West End central police station, Cox and Jenkins were "helping Scotland Yard with their inquiries," as the police invariably say here. They sang sweetly enough to tell where the rest of the tapes were hidden.

It is a safe bet that his hit and errors will now be carefully studied, both in executive suites and underworld pariors.