WHEN POLICE in New York, and later Washington, set up phony fencing operations to trap run-of-the-mill burglars and street thugs, the country loved it. Everyone seemed to get a kick out of watching videotapes of toughs handing over stolen television sets and jewelry, grinning and cracking jokes with cops while the unseen camera rolled on.

And the climax, when the crooks were summoned for a "party" and then were rounded up one by one, was a socko finish. It reminded people of the upbeat feeling they had at the end of the Robert Redford-Paul Newman movie when the ragtime music surged and the bad guys got their comeuppance. Everyone began to call all these role-playing, dress-up, turn-the-tables operations "stings."

It's time to abandon the word. It has come to be used in a way that masks important distinctions among various kinds of law enforcement techniques. It's too frivolous for serious and dangerous undercover police work and too benign for the government entrapment some charge is always part of these operations.

When a California jury acquitted John DeLorean on eight charges of conspiracy and drug dealing, Attorney General William French Smith was asked whether the government would be deterred in the future from using "sting" operations. Not at all, he said. "Undercover operations are one of the most effective and successful investigative tools available today in the war against organized crime, drug trafficking, bribery and public corruption. In many cases, it is the only method of combating these evils."

He is right, of course, and the undercover work by the FBI in Chicago that was revealed recently is a good example of how such an operation can work. Agents infiltrated a continuing criminal conspiracy and over a four-year period, using false identities, government money, disguises and videotapes, accumulated evidence that is said to implicate police and mob figures in prostitution, narcotics and extortion rackets involving tens of millions of dollars.

If the word "sting" hadn't been available when the question was proposed to the attorney general, however, he might have been asked a much tougher, and more pointed question: "Did the government create a crime in order to entrap John DeLorean, and if so, what steps will you take to see that this does not happen again?"

Judge Robert M. Takasugi, who presided at the DeLorean trial, set out the elements of entrapment for the jury to consider. The jurors must find the defendant not guilty, said the judge, 1)if the idea for the crime came from the creative acts of government agents or informers; 2)if the agents then induced the defendant into the crime; and 3)if the defendant had not been ready and willing to commit the crime before he was induced to do so. Some of the jurors believed, on the basis of the evidence presented at trial, that the government had entrapped John DeLorean, and that was a serious, unacceptable invasion of his rights so unlawful as to invalidate the government's case altogether.

It is easy to applaud law enforcement projects, often both tedious and dangerous, when they involve undercover operations to obtain evidence of crime that is in progress or under investigation. It is also right, however, that our laws protect against government-fostered crime that is designed to entrap citizens who would not otherwise commit offenses.

The two situations are very different and profoundly important, both to law enforcement officers and to the public. The distinction should not be muddled by putting them together under the same lighthearted label.