The indictment of a 48-year-old Cuban national in the shooting death of a coworker in a Metro construction tunnel in May has led to a court challenge that Hispanic citizens are under-represented in the District of Columbia jury system.

As a result, H. Carl Moultrie I, chief judge of D.C. Superior Court, has made an unprecedented move by agreeing to allow expenditure of $400 in court funds for a defense expert to investigate composition of the grand jury that charged Guillermo Hernandez Obregon with first-degree murder in July.

Obregon's court-appointed lawyer, Russell F. Canan, contended in court papers that the substantial under-representation of Spanish-surnamed individuals in the pool of Persons available for jury service violated his client's constitutional right to a jury selected from a fair cross-section of the community.

Moultrie made no comment on merits of the claim but agreed that Obregon has a right to court funds to hire an expert to pursue his contention. Since Obregon has been found indigent by the court, his lawyer and the expert will be paid with funds provided under the city's Criminal Justice Act.

According to court records, an initial defense survey of 16,000 question-naires was sent to potential jurors in 1972 and turned up 60 persons with Spanish surnames, only 20 of whom eventually were found qualified to serve. Potential jurors are disqualified or excused from service by the Office of the Jury Commission for various reasons, including medical problems, employment or family responsibilities.

The defense noted that 1970 census figures showed more than 15,000 persons of Spanish origin in the city and that estimates of the Spanish population here have continued to grow in recent years.

In a nine-page opinion on the defense request for expert fees, Moultrie said the evidence collected was substantial enough to prompt an attorney, aided by an expert, to be investigate furthur the grand jury's compostion.

Dr. Charles Turner, an expert in cases involving jury selection and composition, has agreed to assist the defense in the Obregon case and will receive the fee approved by Moultrie, Canan said. Turner is a member of the executive board of the National Jury Project, a research group based in Massachusetts.

Obregon, a laborer who lives in Falls Church, was released to the supervision of a custodian approved by the court in May and has resumed construction work, Canan said.

According to court records, Obregon left Cuba in 1972 and, after a short stay in Spain, came to the United States. Obregon spent about seven years in prison in Cuba between 1962 and 1970 for anti-Castro activities, the records said.

Obregon was arrested May 10 at a Metro construction site at 57th and East Capitol streets after the shooting of Bobby Williams, 41, of 3029 Sheriff Rd. NE.

The government contends in court records that Obregon and Williams had argued that morning, that Obregon later took a gun from his lunch pail and allegedly shot Williams at close range and in front of several witnesses.

Moultrie's opinion approving appointment of the expert witness in the case was issued last month, and the case is set for trial Jan. 22. The defense asked this week for continuance of the case because of difficulties in obtaining lists of potential grand jurors in connection with its research on jury compostion.