A spy ring that operated as long as the one that was finally shut down this week with the arrest of a retired U.S. Army sergeant in West Germany is bound to have left America and it allies with some big chinks in their armor.

Just how big can only be guessed at. But the fact that it operated for eight years indicates the seriousness of the case. So does the fact that former sergeant Clyde Lee Conrad had access to secret plans for the defense of Europe. So do reports that he received a total of two million marks, or more than $1 million; the Soviets and their cohorts don't pay spies that much without getting important secrets in return.No wonder this episode is being described as possibly one of the most damaging espionage cases in U.S. history. Consequently, if Conrad is convicted, the stiffness of his penalty ought to match the seriousness of the crime.

But don't count on it. Since espionage is not covered by Washington's exradition treaty with Bonn, the Conrad case evidently is going to be left in the hands of West Germany authorities and Europe doesn't treat spying as stringently as the U.S. does.

Even in U.S. courts, only one of every five convicted spies gets as much as a life sentence. Three in five get prison sentences of only about 20 years.

The penalty for spying should be stiffer. A robber who kills a clerk while holding up a grocery store may be executed. Why should the penalty be less for someone whose perfidy can jeopardize the lives of multitudes in the event of war and the future of entire nations?

Meanwhile, the U.S. could use more spy-chasers. Former CIA deputy Bobby Inman has warned that the Navy, for example, has three times as many people looking for $600 ashtrays as it does investigating Soviet espionage.

Moreover, America still needs to sharply curtail the number of people it lets in on important secrets. By one authoritative count, some 4.2 million Americans have access to sensitive data - an absurdly large number. Fewer people handling classified documents would mean less leakage. It also would facilitate more frequent and thorough investigations of people with security clearances.

In any event, the exposure of yet another communist spy ring shows the Kremlin is as determined as ever to poke holes in the Free World's armor. How's that again about how the Kremlin, under Mikhail Gorbachev, is supposed to have become less aggressive and more peace-loving?