BRIEF NOTES today on three cats, one alive, one dead and one probable, and then with your kind indulgence we shall close the correspondence on cats.

Now Mosby was that Kennedy Center cat who so loved the place that he let it get built around him (he may well have been in situ for the groundbreaking Dec. 2, 1964) and never left until the occassion of President Carter's inaugural ball in 1976.

I do not, myself, regard his exit as a political statement. Mosby was right there for the Nixon inaugural ball, after all, and if that jam-packed mass didn't drive him out, I don't see how Carter's party did.

It is mentioned only to fix the date.

A reasonable supposition, my own, is that he was squashed by a limousine occupied by some secretary-to-be who was probably stopping smoking about that time and there fore antsy.

Others say he just got tired of the Kennedy Center after all those years - a likely story - and still others say, more plausibly, that once he got out of the building he never could figure how to get back in.

It is generally supposed that all those wooden alleys temporarily set up in the grand foyer were installed to lure Mosby back. They are ideal for polishing cat claws.

Few people ever saw Mosby during his incumbency, and Beppie Noyes, in her definitive work, "Mosby, the Kennedy Center Cat" (Acropolis Books Ltd.) regrets she never laid eyes on him.

"I used to sit up there four hours," she said, "hoping to catch a glimpse of him, knowing he was there, but I never did. I heard him, however."

So did Barbara Bel Geddes and other light fantasticals of the Kennedy Center theaters. Mosby had a nest some feet above the president's box and from time to time perched up there for an evening of catharsis, as you might say. Sometimes he meowed at the wrong times (or so actors complained) and on several occassions Roger L. Stevens, chairman of the center's board since 1961 and never yet charged with felinophilia, ordered the cat to be evicted.

"Don't tell me how, just do it," he used to quip to Ed Schlesser, building manager, whose duties include bruntbearing. Of course Schlesser was probably responsible for Mosby in the first place.

"Even before they pull the center's steel work up," he said. "I used to drive up to the site, early in the day while it was still dark. In my headlights I could see the eyes of cats - oh, there must have been 40 to 60 of them."

The cats of Washington have a general density of 723 per acre, but only about 100 per acre on unoccupied land, hence about 60 surviving at the building site despite jack hammers, bulldozers and rocks chunked by construction workers. This remnant was fed by Schlesser.

"I bought three or four cases of cat food a week, with my own money, and so help me God, I'd see mother cats lugging rats as big as they were to feed their kittens. Watergate was infested with rats, but we never did have any once Mosby got going. Right now we have a lot of mice, now that he's gone."

Schlesser said he suspects Mosby was born about 1964 and that the center was sort of built around him while was a little bitty cat.

Noyes speculates his littermates and his mother moved along (as the other 60 cats did) once they started slopping concrete and so on, but Mosby got left behind.

Anyway, he was fond of lobster, and ate his ever-loving share of it at various notable receptions. He knew how to get his and get out before distraught chefs and caterers knew what hit them.

Mosby lived in that unfinished theater up top in the center, at first befriended by a secretary named Jan. "We don't know her last name," said Ceci Carusi, vice chairman of Friends of the Kennedy Center, to whom the Mosby book is dedicated."She just vanished." Schlesser inherited the pleasant task of feeding the cat.

Among the amusing incidents he could recall, he once broke a number of bones in his foot, taking Mosby's supper up to him, and was in a cast for some time.

The publishers and the Friends got together to put on a reception this week honoring the author, and there were incredible quantities of cheese and fine fellowhip.

Noyes' husband, Newbold, former editor of The Washington Star, said there was nothin like Washington but then there was nothing like Harvard, Mass., either. He said life is fine up there with visits from the grandchildren, and time to write essays. He doesn't like any of the ones he's written, he said, but someone thoughtfully pointted out they're probably a lot better than an editor would know. Like many men, he is handsomer since his retirement from the mines.

The book does not tax the brain and does not once mention the Soviet Union, double-digit anything or the evils of tobacco. Indeed, the Friends of Kennedy Carter think it would be nice for every member to buy 10 copies and give them to tots.

But mark you, those now out of strollers will also find as comprehensive an account of the cats as they are likely to require. In a nutshell, as Schlesser said, "He was a very smart person."

I have always said that if you're going to get into cats at all, you may as well go whole hog, and you will want to know that the British Embassy cat, Bluffy, is alive and well on those nice portico pavements that architect Lutyens arranged for His or Her Majesty's ambassadors on Mass. Ave.

As you know, Muffin died. Muffin was the white cat, mentioned in this space previously. He is, as reported, in harp country now.

But Bluffy is the cat known perhaps to more people than Muffin was. Bluffy is the embassy cat that on occasion has rubbed legs of diners underneath the tablecloth, etc.

Ambassador Peter Jay amplifies - this is not actually a correction, as I trust you understand - that while Muffin had been at the embassy forever, no doubt, still he never quite knew whom Muffin belonged to. It is understand that while Muffin may have got into the embassy on occasion and, for all anyone knows, got under the table, nevertheless it was Bluffy, not Muffin, who is the one with the abbreviated tail (whether lost to a lawn mower or not is still uncertain).

Jay said Bluffy has spent more time in the embassy than any other living creature, and he toated the cat only last week as a notable institution.

Through some sort of communicable error, in other words, Muffin was incorrectly identified as the cat with an imitation Manx tail and the other qualities of Bluffy who, thank God, yet alives.

Bluffy, the ambassador further stated, is 17 years old and was acquired at a Hickory Hill fete. Hickory Hill was the home of the late Sen. Robert Kennedy. Hickory Hill has always had animals, including that notable one that a repairman thought was a fur rug and stepped on.

Once in British territory, Bluffy settled right in and, Jay states, has viewed each succeeding ambassador with increasing disdain.

I did inquire if Bluffy might possible be in very poor health, liable to lay the burden down any day now, but the ambassador said not at all.