Scotland Yard announced today that officers from its special police firearms branch armed with modified submachine guns, will be deployed at Heathrow Airport here beginning Thursday.

The decision to send the police D11, or "Blue Beret," unit to Heathrow marks the first time armed, uniformed officers have been assigned to regular, overt police duties on the British mainland. A Scotland Yard statement said it came after "recent events in Rome and Vienna" indicated a "need to further enhance our ability to protect the traveling public at Heathrow from a terrorist attack."

Since the Dec. 27 attacks at the Rome and Vienna airports in which 19 people died and dozens were wounded, regular British Army units have been on patrol at Heathrow in anticipation of further terrorist assaults. Those units will be withdrawn Thursday, and replaced by the Blue Berets.

The officers of D11, a unit numbering about four dozen men, serve as firearms instructors for the London area Metropolitan Police, or Scotland Yard, as well as performing special security duties.

They will carry West German-made 9-mm Heckler and Koch police carbines, adapted to single-shot rather than automatic firing. British police -- with the exception of the Blue Beret force -- normally are not issued guns, and individual operations requiring firearms must be approved, and the guns issued, by divisional police commanders.