The co-pilot believed to have been at the controls of Continental Flight 1713 that crashed in a snowstorm in Denver last week would not have been allowed to handle the takeoff at American or Eastern Airlines, officials said. Under rules implemented by these two airlines, captains must log at least 100 hours in a specific type of aircraft before they may allow the first officer to attempt takeoffs or landings. Capt. Frank Zvonek, 43, of Carlsbad, Calif., had only 33 hours and 23 minutes as captain of a DC-9, and evidence indicates that co-pilot Lee Bruecher, 26, of Houston was at the controls when it crashed. Bruecher had only 36 hours and 36 minutes in the DC-9.