A federal grand jury has issued a subpoena to Washington Mayor Marion Barry after he did not respond in the last two weeks to an invitation from federal prosecutors to testify, sources told the Washington Post. Meanwhile, Barry has hired R. Kenneth Mundy, a private criminal defense lawyer, to represent him in the probe. In two previous grand jury investigations that touched on his activities, Barry relied on his city-paid legal counsel, Herbert O. Reid Sr., for advice. Mundy said that he received a subpoena for Barry and that the mayor intends to testify. The grand jury is investigating alleged drug activity at a downtown hotel room that Barry visited.