Hearings begin today on one of the most enduring, divisive District debates this decade: the city employe residency requirement.

Officials of several unions representing the District's 42,000 employes have said they will testify in support of an amendment introduced by Hilda H.M. Mason (Statehood-At Large) that would replace the mandatory residency rule with a "preference" for applicants who live in the city. The hearings are sponsored by the council's Government Operations Committee.

The law now requires new hires either to be District residents or to move into the city within 180 days, and mandates that employes who live in the city must remain. Exempt from the rule are all employes hired before 1980, and all data processors, top financial managers, medical personnel at the D.C. Village nursing home and workers at facilities outside the city, such as the Lorton Reformatory.

"We think the position on residency is appropriate as it stands now," said Theodore Thornton, D.C. personnel director.

If the city found itself in dire need of certain categories of employes, "we would go forward through the existing mechanism" of requesting special exceptions from the council, Thornton said.

As a D.C. Council member in the late 1970s, Marion Barry vehemently advocated residency. Shortly after taking office as mayor, however, Barry faced crucial shortages for certain positions and sought help from the council, which granted specific requests but retained its power to make exceptions.

In the city's report on residency this year, department heads told of troublesome shortages in positions as varied as industrial hygienists, entry-level auditors, experienced appraisers, plasterers, engineers and electricians.

Council member Charlene Drew Jarvis (D-Ward 4), a "strong supporter" of the residency rule, plans to propose today an exemption for pediatric nurses at D.C. General Hospital, according to spokeswoman Dawn Alexander. Jarvis and Council members John Ray (D-At Large), Nadine P. Winter (D-Ward 6) and Carol Schwartz (R-At Large) serve on the Government Operations Committee, which is headed by Betty Ann Kane (D-At Large). Ray cosponsored Mason's amendment. Schwartz said she supports the Mason amendment but believes that employes in policy-making positions should be required to live in the District.

Many of the arguments over the residency requirement have persisted since its inception. Originally, D.C. lawmakers wanted to assert a city identity, battle unemployment and assure some correspondence between the racial composition of the city's employes and its residents. And while Congress forbids the District's establishment of a tariff on commuters who work in the city and live in the suburbs, the residency requirement guarantees that government payroll dollars yield city revenue.

But employes and their representatives say they will argue today that the requirement vastly limits the pool of good employes, encourages them to defect to suburban jobs and levies hardships on those who stay and try to find affordable housing.

"It's an economic and a fairness issue," said Tom Tippett, president of Local 36 of the International Association of Fire Fighters.

The need for reform is rising, Tippett said, because 40 percent of firefighters will be eligible for retirement in the next two years. In the meantime, he said, surrounding jurisdictions with no residency rules may well recruit the area's best candidates.

A report on the city's school system prepared by the Washington Lawyers' Committee for Civil Rights raised similar fears over the 600 teaching vacancies that the city expects over the next two years. "Although many other cities have residency requirements for municipal employees, almost none impose it on teachers," the report stated. In the case of the District, higher pay and lower housing costs routinely take away good teachers to the suburbs, the report said.

"We're losing experienced officers," said Pete Carroll, chairman of the Fraternal Order of Police's residency committee, noting that 2,000 of the city's 3,850-member police force will reach retirement age over the next five years. District officers, who are required to carry their badge and gun whenever they are in the city, can find peace of mind and cheaper housing in the suburbs, he said.

But Ron Hampton, president of the D.C. Afro-American Police Officers Association, said that city neighborhoods benefit from having police officers as residents, and called the rule a "cost-effective way to bring blacks onto the police force. "I remember before, when residency didn't count," said Hampton, a 15-year-veteran. "There were D.C. residents looking for jobs, but {police officials} were recruiting people out of West Virginia, with a lot of excuses why."