This episode's headline: Terrorism View from Europe; Guarding the Airports; Undetectable Guns?; Guarding the Capitol; Helping Hands. The guests include In Washington: DOUGLAS HURD, Home Secretary, Britain; Rep. ROBERT MRAZEK, Democrat, New York; JAMES BAKER, National Rifle Association; In New York: DAVID BYRON, Inventor; REPORTS FROM NEWSHOUR CORRESPONDENTS: TOM BEARDEN; RICHARD COHEN, in Washington. Byline: In New York: CHARLAYNE HUNTER-GAULT, Correspondent; In Washington: JIM LEHRER, Associate Editor