Commerce Secretary Ron Brown's plane has crashed near Dubrovnik, Croatia, in bad weather and there are reports at presstime that Mr. Brown, some government officials and executives traveling with the secretary have died. Mr. Brown, 54, had been on a trip exploring business possibilities in the Balkans. The initial indication was the crash was weather-related. There was some confusion on the list of executives aboard as rescue teams search for the plane. It appeared, however, that no executive of consumer marketing companies were there. Northwest Airlines Co-Chairman Al Checchi had once been listed as planning to go.