Whenever an accomplished journalist such as Tad Szulc turns his hand to fiction for the first time, there is the hope that the novel, especially if it is one of international intrigue, will be riveting and gripping and all the other fine things that publishers like to quote in their blurbs.

Unfortunately, "Diplomatic Immunity" is rather so-so, almost bland, and the characters who people this tale of U.S. involvement in a Central American revolution are predictable to the point of exasperation -- like old neighbors with irritating habits.

Julia Savage is the beautiful, 36-year-old workaholic ambassador the administration in Washington has dispatched to deal with the West Point-educated, right-wing dictator in the Republic of Malagua, which Szulc might as well have called by its real name, Nicaragua.

The divorced Savage is a political appointee, and a liberal at that, which leaves a brown taste in the mouths of the old-line State Department crowd. No warmer welcome awaits her in Malagua from the wicked, cigar-chomping CIA station chief, Jim Morgan, a crony of dictator Juan Ferrer.

Savage's mission, it seems, is to keep the country from becoming "another Cuba." She is instructed to work with dictator Ferrer toward a "gentle democratization," whatever that means.

We are assured that Ambassador Savage's qualifications to accomplish this not inconsiderable task include not only her extensive education, but also the fact that she is both powerful and beautiful. In the "jaded capital" of Washington, Szulc assures us, this is an "extraordinary combination." Furthermore, he gossips, Savage was "on almost every important invitation list, from Georgetown to Embassy Row, and she regularly made the society pages of The Washington Post and The Washington Star."

Thus convinced early on of Madame Ambassador's qualifications, I immediately got the feeling that prospects for the impoverished Malaguans must be looking up. But wait. Since the ambassador is beautiful, surely there must be someone for her to fall in love with. The wicked CIA station chief? An interesting twist. But it is not to be. Taken as her lover is none other than a revolutionary Catholic priest, a Jesuit at that, who conveniently is just on the point of renouncing his faith.

Well, these two do fall in love and they do go through a love scene or two, which demonstrates, I think, why someone was bound to come up with the phrase "obligatory sex." I can't believe that Szulc's heart was really in it when he wrote that the priest "held her hand a moment longer and a little harder, their eyes looking for an instant into eternity . . . Asturias the priest thought she was the most marvelous sight he had seen in a very long time." It gets a bit steamier after that, but not much.

The CIA station chief conspires against Ambassador Savage by forcing his cocaine-smuggling Colombian partner -- who just happens to be her ex-husband -- into blackmailing Savage with the threat of revealing to the world the awful fact that long ago she once harbored overnight a Weatherman -- or person, as the case may be.

But Savage quite sensibly tells her ex-husband to buzz off and sets about her task of keeping the country from going the way of Cuba. She is aided in this good deed by the revolutionaries themselves when they take over the country's National Assembly and hold all its members hostage, including Savage, who conveniently has dropped by that day.

After much hemming and hawing from Washington, Savage is named the principal negotiator between the dictator and the hostage-holding revolutionaries. A key segment of the army then throws in its lot with the rebels and the dictator wisely takes the next plane out.

But just when everything seems to be going swimmingly for the new government, the perfidious CIA strikes again, forcing Ambassador Savage to make an agonizing choice, which she does, sensible to the end.

Szulc has written a conventional novel with a plot quite legitimately torn from recent headlines. Such novels can sometimes illuminate dark political corners to the reader's enlightenment and immense satisfaction. Perhaps this is what Szulc intended to do. It's regrettable that he didn't.