If necessity is the mother of invention then Fiona FitzGerald, whose third incarnation is now appearing in Immaculate Deception, must be the granddaughter of necessity.

She was created out of the compulsive need to "create" which surely afflicts all novelists. Add to that need the fear of time's relentlessness and you have the perfect prescription for the disease of "prolificism," an affliction that currently rages in my brain cells.

As mostly a "mainstream" novelist with no genre orientation, I was faced with a complicated dilemma back ten years ago. I was producing too many novels for the marketing boys and girls in the hardback publishing business to absorb effectively.

Worse, I felt the compulsive need to pursue a daily routine of novel writing, a kind of manic race with time, triggered by my late start as a published novelist.

It had taken me until I was over forty to publish my first novel, or, put another way, I had tried for nearly a quarter of a century to get my work published. It never ceases to amaze me that the fire to write has burned so brightly for, as they say, lo those many years. But burn it did.

Being finally published, triggered an atomic conflagration in my psyche and, having given up all other pursuits but writing, I proceeded to embark on a furious campaign of "catch up" which continues to this day. (Eighteen published novels in sixteen years.)

Also at that point in my life, I had lived in the nation's capital for nearly thirty years and was an active participant in its heady political and social life. Indeed, one of the businesses founded by my wife and I in my pre-novel business life had been the Washington Dossier, the monthly society magazine that tracked the comings and goings of the people in the Washington power arena. I had a ringside seat at the spectacle, providing material that ached to be recycled in novels.

But since the publishers couldn't very well market mainstream novels at the furious pace that I was writing them, I determined, like many fellow writers to pursue a parallel career as a mystery novelist, of which Evan Hunter/Ed McBaine is the prime example. Frankly, I felt the compelling need to get this Washington stuff recycled into novels.

Thus, Fiona FitzGerald, the protagonist of the mystery series that began with American Quartet in 1982 was born. I hope she is something of an original.

She is an elegant lady in her mid-thirties, whose father was once an important Senator. She has chosen to ply her trade as a homicide detective in the most pressurized, black dominated police department in the world, the Washington D.C. police force, MPD.

She has been raised in Washington in the lap of luxury and in the vortex of power. She is an integral part of the social fabric of the Washington elite. Because of this background her boss, Homicide Captain Luther Greene, affectionately dubbed "the eggplant" (behind his back, of course) assigns her to those cases of murder that happen on Fiona's natural turf.

Thus, we have the modus operandi of this series, which, at its heart is an authentic exploration of what is really happening behind the mask of power.

Through insight, intuition and background, Fiona is fully equipped to match wits with those who run the power establishment. She understands the motivations and mores of Washington's most important players: Senators, Congressmen, Judges, Generals, Administration figures and social doyens.

Invariably, her actions are played out against the background of the "big questions." Fiona leads our readers through the thickets of politics, power and ambition that run the locomotive of American democracy.

But while the larger questions are always there, Fiona continues to face her own struggle to find her place in the world she has chosen. In her homicide role as the only white woman on the squad, she must cope, for example, with the inevitable struggles of class and racial hostility.

As an attractive and independent single woman, she also has to deal with her sexuality, her natural desire to forge a relationship in a town where ambition plays havoc with the male libido.

To cop a phrase from Kipling, she sits exactly where "the twain meet." Through her eyes we see the inner workings of today's Washington, the nobility and chicanery, the wisdom and the folly. For me, who lived in Washington and circulated in it's social and power world for more than thirty years, the Fiona books represent an enormous challenge to get it right.

My hang-up was that I didn't want to write these Fiona books under a pseudonym. Against the advice of publishers, agents and book marketers, I determined that having suffered years of the slings and arrows of rejection, I would write under my own name and let the chips fall where they may.

In 1991, they are indeed falling all over the place. Two Fiona books will be published this year: Immaculate Deception in February and Senator Love in August from Donald I. Fine, Publishers. When we headed up Arbor House, we had published the first two books in the series American Quartet and American Sextet.

In April, my mainstream novel, Private Lies, will be published by Morrow to much promotional fanfare. How these novels will react with each other from a marketing standpoint will determine if my decision was a wise one.