Washington labor union leaders won a preliminary round yesterday in an effort to delay a city council committee's scheduled approval today of a major new personnel system for municipal employees.

Robert E. Petersen, president of the 200,000-member Grezter Washington Central Labor Council, AFL-CIO, was joined at a news conference by three other union spokesmen, with all of them demanding a one-year lag in adopting the measure. They contended the bill would remove protection for city employees and might lead some to walk off their jobs.

By late afternoon, all five members of the Council's Government Operations Committee said they would be willing to defer action today - but most said the time would be much shorter, no more than a month.

The complex measure, which has been on the drawing boards for more than two years, would put all but a few of the 40,000 city employees under new personal systems administered by the city and its educational institutions. All employees would be phased into a single salary schedule, separate from federal pay scales.

At present, there are separate personnel policies covering police, fire-gighters, teachers and the large group of other city employees, with many of them covered by U.S. Civil Service Commission rules and the federal pay system.

The city's Home Rule Charter requires the city to have its own municipal personnel system in operation by 1980. Officials say at least a year would be needed between its adoption by the Council and its effective date.

Council member Arrington Dixon (D-four), chairman of the Government Operations Committee, said he "would be willing to delay for a reasonable duration . . . to take another look" at the union objections. He strongly defended the measure as drafted, saying it meets the city's needs "even if it will not meet any one group's personal or biased interests."

Even before yesterday's union news conference, Council member Marion Barry (D-at large) said he had asked Dixon to agree to a one-month delay. Douglas E. Moore (D-at large) said he would make a motion for a delay, and Hilda H. Mason (Statehood-at large) and William I. Spaulding (D-five) said they would support further consideration.

Peterson was joined at the news conference by David A. Ryan, president of the Fire Fighters Association; William Simons, president of the Teachers Union, and Donald M. MacIntyre, a vice president of the American Federation of Government Employees.

Peterson complained that the bill lacks an equitable job-classification system, that the compensation system is not adequately spelled out and that the right of collective bargaining over wages has been gutted. Ryan demanded the retention of binding arbitration over wages.

If the bill is passed, Peterson said, "the probability of wildcat (unauthorized) job actions and strikes will be very high."