Twelve persons -- all members of an informal ring of acquaintances -- have been arrested on charges of cashing an undetermined number of stolen witness payment vouchers from D.C. Superior Court.

The thefts, which occurred piecemeal during much of 1979, have netted the group at least $1,500 in illegal payments and led to the firing of a secretary in the U.S. attorney's office at the courthouse. She was suspected of supplying members of the ring with some of the forms, D.C. police said yesterday.

An investigation, which began in April 1979, is continuing and more arrests are expected, police said.

At least 60 vouchers have been recovered thus far by police. About half of them were cashed by members of the group, mostly residents of the Barry Farms public housing project in Southeast Washington, police said. At least 60 vouchers have been recovered thus far by police.

Other vouchers were spotted and intercepted by sharp-eyed court finance office clerks who normally cash the vouchers. In two instances they suspected that the names of assistant U.S. attorneys had been forged on the vouchers by "witnesses" seeking to cash them, police said. The clerks called police, and the suspects were arrested on the spot.

The vouchers, which are kept in the U.S. attorney's office, are used to pay witnesses $30 for each day they report to court trials, grand jury hearings or pretrial conferences. The forms, which must be signed by an assistant U.S. attorney, indicate the number of days the witness appeared in court before they can be cashed.

The fraudulent forms usually were made out for five days, allowing a person to collect $150 and calling for emergency payments, allowing payment in cash instead of waiting for the government to mail a check, D.C. police said.

Since the thefts, security has been tightened in both the U.S. attorney's office and the courts' finance offices. All payments are now made by check.

According to detectives in the check and fraud unit of the police department, leaders of the group were witnesses to a homicide and became familiar with the voucher system while reporting to the U.S. attorney's office in connection with the upcoming trial in that case.

Since "there was just no control" over the vouchers in the prosecutor's office and the vouchers were almost everywhere," the ringleaders simply helped themselves, said Detective John Malkiewicz, who is in charge of the investigation.

The leaders then gave the form to friends in the Barry Farm project, police said.

When the leaders could no longer simply walk into the office and pick up the forms, a secretary working in the prosecutor's office obtained some of the forms for them, according to police. The secreatry was fired, but no charges have been placed against her, police said.

Those arrested and charged with passing falsified documents are Eula B. Cooper, 25, of 1114 Sumner Rd. SE, Jacqueline Craig, 19, Theresa Butler, 22, and Columbus Keemer, 22, all of 2616 Firth Sterling Ave. SE; Rodney Blanton, 24, of 1118 Sumner Rd. SE; Donna Prailor, 27, of 1220 Sumner Rd. SE, and Jeannetta Haygood, of 1310 Sixth St. NW. Four juveniles also were charged in the case, police said. Prosecutors said a 12th person pleaded guilty to similar charges earlier this year, but the name was unavailable.