"Ooh," sighed the British lady from the posh PR firm that "lets" Leeds Castle, why the place is simply teeming with nasty dogs and men with horrible rifles."

Of course, that Saxon named Leed (or Led or Ledian - no one's quite sure - he wasn't much for writing) discovered 1,100 years ago what Scotland Yard decided over the weekend: Leeds castle in the Kentish countryside 45 miles south of London, picturesque, serene, majesticc is, above all, secure . Scotland Yard is nobody's dope, dope.

Which is threats of terrorism in London turned a nervous security community's attention southward to Leeds Castle as the site of the talks beginning today between Israeli Foreign Minister Moshe Dayan and his Egyptian counterparts Ibrahim Kamel.

Over its lifetime - 300 years of which were spent in the hands of British royalty, mostly British queens - Leeds was strengthened and fortified and strengthened again so that even should its natural defenses (sole access is across a narrow drawbridge over its lake) be breached, its thick stone walls, 6-feet in some places courtesy Henry VIII, make it as impenetrable a bastion as Scotland Yard or British Prime Minister James Callaghan could want for the Mideast peace talks.

"Yes," the lady from Clark, Nelson pronounced yesterday, "I'm giving away no secrets because it's all been on the telly all weekend, but Callaghan was getting this continuing stream of messages warning about trouble and then there was that poor Iraqi fellow (actually Gen. Abdul Razzak Al Naif, former prime minister of Iraq) who was shot, poor man, in Park Lane . . . And with these talks on fire to begin with, well, what could they do?"

Clark, Nelson, international public relations, has as a client the Trustees of Leeds Castle, bequeathed in all its secure glory to the empire by its last private owner, the Hon. Olive, Lady Baillie.

Here is no vacant, cold, medieval museum. For 50 years Lady Baillie, American (Whitney) heiress married to a British lord, lavished virtually limitless funds, and, with the aid of noted decorator Stephan Boudin, made her life's work the restoration and refurbishing of the historic castle in the lush green Kent countryside. As she collected medieval tapestries, Gothic stairways, Renaissance art, she also had installed the most opulent of modern conveniences so that her children, her guests at a virtually endless round of parties and, during World War II, recuperating wounded Allied servicemen, lived in surrounds as luxurious as they were authentic.

"There was a bit of riding - and the men shot, of course, and golf and croquet and squash," recalled one of Lady Baillie's daughters recently at the castle on the occasion of the reconsecration of the 700-year-old chapel which had gone "used for everyday things" for the past several centuries. The Archbiship of Canterbury was there and so was Princess Alexandra, daughter of the late Duke of Kent and Queen Elizabeth's cousin.

In her bequest, Lady Baillie expressed the hope that the castle would be the site of great medical conferences.

But no one could imagine that a peace talk or two would distress the resident peacocks, geese and haughty black swans any more than would a covey of doctors.

And Leeds is splendidly appointed for conferring: A mammoth oval conference table in a room overlooking the lake, the sailing swans, the rolling Kent hills. In addition there are the living quarters for conferees as well as for valets, maids and any entrourage that might happen along, all in the finest tradition of English country houses.

The lady from Clark, Nelson called it "an American do," these "fiery talks," but conceded that "we're having it (televised) nationwide, of course," and if there was ever a place to put out a fire . . .