Maryland and District of Columbia officials continued to monitor radiation levels in air, water and milk samples yesterday and reported finding "no significant increase" in normal radiation readings following the accident at the nuclear power plant near Harrisburg, Pa.

While authorities here repeated assurances to area residents that the problems at the Three Mile Island plant pose no hazard to them, civil defense officials started drawing up contingency plans in the event that Pennsylvania residents living near the nuclear power facility are evacuated into Maryland.

"There is no need for any immediate action [to take care of any evacuees] and the odds are there never will be," said Gene Oishi, press aide to Maryland Gov. Harry R. Hughes.

Oishi said Hughes had met Saturday with about a dozen of his department heads in an attempt to assess radiation monitoring procedures and to plan how to take care of an influx of people into the state if evacuations from the area around the plant become necessary.

Civil defense directors in Cecil, Harford and Baltimore counties-along the Pennyslvania border-are identifying churches, civic halls and schools that might be able to house Pennsylvania residents, Oishi siad.

Max Eisenberg, acting director of Maryland's Department of Environmental Health Services, said yesterday that Scientific checks of air, of the Susquehanna River water that flows into Maryland from Pennsylvania and of milk delivered here from dairy farms near the Three Mile Island plant "show no increase above normal" in radiation levels.

In addition, Eisenberg said, state radiation officials took further air samples during a helicopter flight yesterday morning along the Maryland Pennsylvania border. These test, too. showed no hazardous increase in radiation levels.

District of Columbia authorities have been monitoring air and water samples for radiation since Friday and plan ot start taking milk samples today. according to Herbert L. Tucker, director of the D.C. Department of Environmental Services.

Area weather authorities also noted yesterday that there is no indication that radiation contamination in the air around the plant site is being blown in the direction of Washington.

Meanwhile the Potomac Alliance, a Washington-based antinuclear group, met yesterday and began drafting plans for a demonstration here next Sunday and Monday to protest conditions at the Three Mile plant.