A quadriplegic has been charged here with murdering his wife of two weeks by using his mouth to yank a string that was attached to the trigger of a handgun. Witnesses told the police that his wife had placed the string in his mouth just moments before.

The 37-year-old victim, Bertha Mae Burns, was slain Monday night at a bar where she and her wheelchair-bound husband, James B. Burns, 40, had been talking. The police described the weapon that killed her as a 9-millimeter pistol mounted on a small board that Mr. Burns had across his lap. A string ran around two small screws in the board, they said, with one end of the string running to the trigger. A shoebox that had covered the entire apparatus was removed before the shooting.

Mr. Burns was upset because his wife was planning to live in California and also because he suspected her of infidelity, the police said.

''According to witnesses, they were sitting there talking in quiet tones,'' said a police detective, A. J. Toepel. ''She then got up and put a string in his mouth, and he jerked his head back once and the gun went off.'' 'Talked Me Into Killing Her'