"The Amateur," an espionage thriller that dispatches an average chap on a mission to make a citizen's assassination of the terrorists who killed his fiance', makes impossible demands of both its hero and viewers. It should have been terminated with extreme prejudice.

Such a judgment may be somewhat unfair. It would wipe out a couple of splashy chase-execution scenes and the performance of Christopher Plummer as a rumpled Czech scholar-spy who puzzles over Elizabethan ciphers and ardently believes Francis Bacon wrote Shakespeare's plays and poetry. But then there's no room for sentiment in the espionage trade.

Our amateur agent without a license to kill is Charles Heller, a quiet, introspective computer cryptologist for the CIA. He takes on the Russians, the Czechs, the CIA and a trio of fanatical Moscow-trained terrorists after his girlfriend is murdered as a sacrificial hostage during the takeover of the American consulate in Munich.

Viewers are asked to believe that Heller, who blackmails the CIA to give him some rudimentary training as an agent-assassin, can carry out his vendetta of personal revenge in the dangerous world of international espionage and terrorism. It becomes a mission impossible to suspend disbelief through a series of serendipitous escapes and examples of colossal ineptitute by his professional pursuers.

Among the hunters is the CIA, which professes sympathy but offers no help to Heller in seeking to avenge his fiance''s death. So Heller raids the CIA computer files for material to blackmail the agency into training him to do the job himself. The CIA hopes to keep Heller on a leash until it retrieves the incriminating files and then is free to eliminate the amateur who isn't playing according to the rules of the espionage game.

The movie, which is based on the novel "The Amateur" by Robert Littell (he helped with the screenplay), takes a few passing swipes at raising such questions as an amateur's ability to kill and the need of the ritual of revenge for the survivors. But before anyone can anguish too much over ethical and moral problems, we are back to the chase through the streets of Prague. "The Amateur" leaves such metaphysical probings to the espionage novels of authors like John le Carre' and Graham Greene.

John Savage, who previously appeared as the quadriplegic in "The Deer Hunter" and in "The Onion Field" and "Inside Moves," is cast in the role of Heller. There isn't much more that he can do except be tight-lipped and portray a man grimly determined to get his revenge. Plummer isn't given enough material to develop the character of Professor Lakos, head of Czech intelligence and Elizabethan cipher expert. Marthe Keller looks as if she suffered as the Czech widow who is the CIA contact for Heller in Prague and joins him on his personal mission.

Director Charles Jarrott does achieve a chilling atmosphere in the opening sequence with the terrorists taking over the American consulate and then choosing -- by a draw of the passports -- the hostage who will be the first killed if their demands are not met.

And there is a spectacular execution scene when Heller plants a bomb to kill a terrorist who takes a morning swim in a hotel pool with an underwater viewing glass for bar habitue's to watch bikini-clad mermaids during the cocktail hour. The bomb explodes with a Niagara gush of water, carrying along a bloody corpse.

One or two scenes like this -- the final chase-confrontation is through the mirrored, chandeliered grand foyer of a deserted hotel -- is the most "The Amateur" has to offer.