The chief judge of the D.C. Superior Court has decided to keep the city's arraignment court open longer each day so that as many arrested persons as possible can be brought promptly before a judge for a hearing on their case.

The decision, announced by Chief Judge H. Carl Moultrie in a memorandum to the court's trial judges, apparently is intended to help the city police apartment comply with a federal court order that arrested persons be brought before a judge within four hours of their arrest.

In arriagnment court, an arrested person appears before a judge and enters a plea of guilty orinnocent to the charges against them. Bonds also are set by the judge who sits in arraignment court.

In May Chief Judge William Bryant of the U.S. District Court here ruled that the police department had detained arrested persons for unnecessarily long periods of time before they were brought to court - a violation of their constitutional right to a prompt hearing.

Earlier this month, Bryant agreed to give the department until Dec. 1 to come up with a plan to eliminate the delays. In the meantime, Bryant ordered the police to account in detail for any delays longer than four hours between a person's arrest and his or her appearance in court.

While that order does not apply specifically to the Superior Court. Moultrie's decision appeared to be an effort to help the department meet Bryant's directive.

The effect of Moultrie's decision is to give the police and the local prosecutors an additional half hour on weekdays and 2 1/2 hours on Saturdays to complete the paper work necessary to present an arrested person in court.

Under the previous system, the judge in arriagnment court was required to accept cases ready for presentation by 3:30 p.m. on weekdays and by 9 a.m. on Saturdays. Moultrie in his memorandum released late Friday extended those deadlines to 4 p.m. and 11:30 a.m. respectively, and made the changes effective immediately. Arraignment court is closed on Sundays.

Judge Samuel Block, who is currently assigned to arraignment court, said yesterday that he expected the extra half hour would mean a judge would be on the bench for at least an extra hour to handle the additional defendants who will be brought to court. Last week, before Moultrie's decision, Block said he spent an average of 6 1/2 hours on the bench and heard a total of about 80 cases a day.

Court officials said yesterday that they could not yet estimate the financial impact of Moultrie's decision of employes' salaries. Judges and prosecutors are paid a flat salary, but court clerks and deputy U.S. marshals - who must also be present when arraignment court is a session - are eligible for overtime pay, these officials said.