THERE SEEMS TO BE a sense of genuine surprise at the FBI, the Justice Department and elsewhere that serious criticism has been directed at the law-enforcement techniques used in the Abscam investigation and, apparently, in many other undercover operations. After all, it is said, the kind of deception employed was much like that used in the first Sting operation and hardly anyone complained then. Making this point on the opposite page today, for example, former assistant attorney general Stanley Pottinger writes that an obvious difference is the kind of people at whom the particular investigation was directed -- robbers and thieves, many of them black, in Sting I and public officials and businessmen, most of them white, in Abscam and other operations. But that was neither the only difference, nor the critical one.

In Sting I police officers set up business in a warehouse and passed word around this city's streets that they were prepared to buy stolen goods. The thieves streamed in, haggled over prices, were photographed and, eventually, arrested. Most of the crimes with which they were charged -- burglary, receiving stolen property and gun law violations -- had been committed before they walked into the warehouse.

To parallel that scenario, the agents in the Abscam operation would have had to rent that house on W Street, pass word around in the right circles here (and elsewhere) that they were rich Arabs with immigration problems, and wait. In due course, or so the agents would have hoped, corrupt congressmen or their associates would have sidled up to them with propositions.

That, at least according to what we have been told so far, is not what happened. Sen. Larry Pressler -- remember, he was described by one of those unnamed law-enforcement sources as "an honorable man" -- says he went to that house only after prodding from someone who wanted to give him a campaign contribution. From his story, and those of some of the others caught in the Abscam web, it sounds as if the agents and those working with them were rounding up prospective victims and taking them to the house in the hope that they would commit a crime in front of the video cameras.

That makes two substantial differences between Abscam and Sting I -- how defendants came to meet the undercover agents and whether a prosecutable crime had already been committed when that meeting occurred. Such differences sometimes separate sound police work from illegitimate entrapment.

What was done in Abscam may not be entrapment in a legal sense. High officials of the Justice Department are said to have watched every move carefully to make sure entrapment did not occur. But the line is thin. The government doesn't entrap a person simply by providing the opportunity or the facility for the commission of a crime by someone predisposed to commit it. But entrapment does occur when the crime is the product of the "creative activity" of law-enforcement officials.

In Sting I, the undercover agents rejected offers from thieves to steal any particular item the agents wanted to buy; they feared that would be entrapment. The agents also lost one major case in that operation when a jury believed the agents had been so aggressive in their pursuit of an assistant U.S. attorney that they persuaded him to accept a bribe he would not otherwise have accepted.

It takes only a little too much enthusiasm to turn a legitimate Sting operation into a mechanism that tries to entice law-abiding people into committing crimes that others have fabricated for them to commit. While the FBI should be trying to catch corrupt politicians, businessmen and others by giving them a chance to commit -- on camera -- a crime they would have committed anyway, it must not play both God and the serpent while casting ordinary citizens, or even politicians, as Adam and Eve.

Perhaps the FBI and the Justice Department have done their jobs well, knew that those they targeted were "predisposed" to be bribed, did not entice them into committing crimes that otherwise would not have been committed, and have turned up not only a major political scandal but many other scandals as well. We hope that is so, but it may be wiser to reserve judgment until all the evidence is in. The Pressler story and the reports that not all those named as bribe-takers will be indicted raise doubts.