OF THE FIRST six persons arrested for homicide in the District of Columbia in 1983, two had previously been charged with other murders. Leroy Farley, 25, had been convicted five years ago of beating a man to death with a baseball bat. Because he was sentenced under the Youth Corrections Act, the penalty imposed on him is not known, but whatever it was, he was free when he was arrested and charged with the New Year's Day slaying of a liquor store owner. The other accused is Ester Hairston, a 53-year- old truck driver who last week was charged with the shotgun murder of a woman with whom he was living. He had been free on $3,000 bond since last June awaiting trial for shooting to death the woman he was living with at that time.

Both the police and the U.S. attorney's office say that repeat murders are "not at all uncommon" in this city, even after an offender has served 10 or 12 years in prison for a first crime. In Mr. Farley's case, because the murder for which he was earlier sentenced was committed before his 26th birthday, he was treated under the more lenient Youth Corrections Act and was out in less time than usual. If he is convicted of the liquor store murder, he faces a much more severe term and would deserve it.

Mr. Hairston has not yet been convicted of either murder with which he is charged. But for anyone found guilty of two such crimes, there would hardly be room for the leniency often accorded those who kill without premeditation in the course of a domestic dispute and who are believed to be less dangerous to the public at large.

Meanwhile, the interesting question is why Mr. Hairston was freed on bail after being charged in the first murder. Under the bail law then in force, it was difficult to obtain pretrial detention of persons charged eve with serious crimes like murder. A hearing requiring the production of a great deal of evidence was mandated. Expedited trials had to be granted. That law was recently changed, and the new law was upheld by the District of Columbia Court of Appeals on Dec. 3. Now a person charged with first-degree murder can be held without bond if the safety of the community or his appearance for trial cannot otherwise be guaranteed.

It is this new law that made it easy to hold Mr. Hairston this time, and that will be invoked when Leroy Farley is brought to court to face his new charge. The new law gives the courts an important tool--one they did not have last June--for dealing with some of those considered most dangerous to the safety of the community.