The FBI's cyber crimes unit will help Washington County authorities analyze materials seized from Mr. McKee's home near Hagerstown, an FBI spokesman said yesterday.

"For me, this is deeply embarrassing," Mr. McKee said in a statement faxed to news organizations. "It reflects poorly on my service to the community as a state delegate and as executive director of Big Brothers and Big Sisters of Washington County. Accordingly, I am resigning today from both positions."

In a signed letter to House Speaker Michael Busch, Mr. McKee, a Republican, indicated that his resignation would be effective 8 p.m. Monday, said Alexandra Hughes, a spokeswoman for the speaker.

Washington County Sheriff Douglas Mullendore confirmed that the case is a child pornography investigation. He said investigators conducted the Jan. 31 search of the home after receiving a phone call from someone who told them about child pornography at the residence. He said investigators seized several computers, about 30 video tapes and printed material containing logs of different information.

Sheriff Mullendore said the sheriff's department asked for FBI assistance, partly because the investigation involved a public figure. The cyber crimes unit investigates computer crimes including malicious hacking, child pornography and Internet fraud.

Charges have not been filed, and the sheriff said he did not know when, or if, charges would be filed.

The Washington County Republican Central Committee will make a recommendation to Gov. Martin O'Malley for a replacement, Ms. Hughes said.

Mr. McKee, 58, has served in the House of Delegates since 1995, following his election in 1994. His home is in Halfway, an unincorporated community south of Hagerstown.

Mr. McKee said he has instructed his counsel to cooperate with law enforcement.

"In the meantime, I have entered treatment," Mr. McKee said in the statement. "My primary focus is to get well and stay well. I know this can only happen with the support and prayers of my family and friends and the help of professionals."

Mr. McKee has been chairman of the western Maryland delegation, which is made up of legislators from Carroll, Frederick, Washington, Allegany and Garrett counties. Del. LeRoy Myers, R-Washington, vice chairman of the delegation, said he plans to meet next week with the region's other legislators to select a new chairman.