A former Fairfax County special magistrate who said Chief Special Magistrate Milton Alexander improperly forced him to resign lost a $233,425 civil suit against Alexander yesterday.

The jury verdict came after a three-day trial before Fairfax Circuit judge Richard J. Jamborsky.

The former magistrate, Preston C. Thomas, 60, resigned his position in August 1977, after his wife broke her right hand in a fall. Thomas alleged that he had to resign because Alexander would not give him 17 days of sick leave to take care of his wife.

Alexander, 71, and the father of Fairfax Supervisor Joseph Alexander (D-Lee), had suggested to Thomas that he take three days annual leave, which, together with normal days off, would have given him eight days to care for his injured wife, according to court testimony. Thomas said that wasn't enough time and -- under duress, he alleged -- quit.

Thomas, who has tried unsuccessfully to be reappointed, sought damages equivalent to income and benefits he said he would have received if he had continued as special magistrate until 1984. Magistrates are empowered to receive payments for parking tickets and issue temporary detention orders in commitment cases.

Thomas, who now drives a cab, claimed that Alexander, who also is chief of the Violations Bureau, was improperly appointed to his post as chief magistrate by Fairfax Chief Circuit Court Judge Barnard F. Jennings.

Thomas's attorney, Lois H. Miller, said state law specifies that the chief must be chosen from among full-time magistrates, and that Alexander was not one at the time.

In testimony at the trial, Jennings said the appointment was proper.