Two alleged Ku Klux Klan leaders in Maryland and Delaware were arrested yesterday along with six other persons in connection with what authorities dexcribed as a conspiracy to firebomb the Baltimore County NAACP headquarters.

A spokesman for the federal Bureau of Alcohol, Tobacco and Firearms said it closed an investigation of alleged Klan activity in the Baltimore County area after concluding that firebombing of the NAACP headquarters in Catonsville was, in one agent's words, "imminent."

One of those arrested yesterday in the joint investigation by Baltimore County police and the federal agents was identified as Richard L. Savina, 29, of Baltimore County, described by ATF officials as an "Imperial Wizard" of a Maryland Ku Klux Klan Organization.

Also arrested, ATF officials said, was Charles William Sickles of wilmington, Del., described as Savina's Delaware counterpart.

The ATF said it began investigating the Klan in New England last summer in connection with alleged illegal activities involving fire arms. ATF spokeswoman Dot Koester said information obtained there led to Baltimore County.

According to the ATF, a county undercover officer was given an incendiary device Wednesday that allegedly was to be used at the NAACP office.

Savina was charged with conspiracy to damage property by means of an incendiary device and Sickles with trafficking in firearms. ATF said two handguns were seized at the time of Sickles' arrest. A sawed-off shotgun was seized in Essex, Md., in connection with the arrest of another of the six suspects, ATF reported.