Thirty persons were treated for eye, nose, throat and stomach irritations in a mobile medical unit outside the D.C. Municipal Center yesterday as residue from a tear gas explosion in the building 12 days ago lingered in hallways and offices.

The medical unit was first set up Monday by the D.C. health department. Seventeen of those treated yesterday were members of the 71-man work crew that is attempting to clean up the building.

The members of the work crew, which is made up of employes from the Department of Environmental Services and volunteer inmates from Lorton Reformatory and D.C. half way houses, have been working four-hour shifts wearing disposable body-covering outfits. Most of the crew members treated yesterday had been working on the second floor of the building near where the explosion occurred Jan. 12.

The massive building at 4th and D streets NW has been virtually closed since the explosion in a second floor police ammunition supply room that released fumes from 200 six-ounce containers of tear gas.

Meanwhile, the 10-man task force set up last week by Mayor Walter E. Washington to examine the building and work out procedures for removing the gas residue will meet this morning to determine which offices in the building can be opened in the near future.

The task force will base its decision largely on the results of tests made yesterday by an environmental air sampling machine that can determine how heavily contaminated the building is.

George W. Rodericks, director of the D.C. Office of Emergency Preparedness said yesterday that initial samplings taken from rooms not in the general vicinity of the explosion revealed "positive results."

But reports from persons inside the building yesterday indicated that rooms and corridors on the first, second and third floors on the Indiana Avenue side of the building were still heavily affected.

"There's still a lot of dust in the corridors, especially on the Indiana Avenue side, and when people walk there they'll just walk right through a cloud of the stuff and have to get outslide right away," said John J. Colbert, assistant director of the Office of Emergency Preparedness.

Building employees also are working four-hour shifts, which include 15-minute breaks every hour. The removal of a number of police lockers Monday and yesterday on the second floor stirred the lingering gas residue again.Conditions reportedly were worse on the second and third floors than they had been the past several days.

Many employees remain on leave as a result of the liberal policy worked out between the city government and the union to which municipal employees belong - D.C. Council 20 of the American Federation of State, County and Municipal Employees.