“The Increment,— a new thriller by David Ignatius, would be a fun summer read if it didn’t feel so damn realistic. The novel tells the gripping story of the United States’ inevitable march toward war with Iran, with behind-the-scenes intelligence maneuvering and gripping car chases. It’s so realistic that at times readers can feel as if they’re overhearing real conversations inside the CIA.

Seen in the context of recent news — with reports that Iran last week launched a medium-range nuclear missile — it’s hard to think of “The Increment— as a form of entertainment to distract us from more serious fare.

Ignatius, a Washington Post columnist who has done a fair amount of reporting on the CIA and Iran, lends a nearly creepy verisimilitude to this tale of a disaffected Iranian nuclear engineer, a disaffected CIA honcho, a disaffected British spy, and a downright cynical — and disaffected — Lebanese arms dealer.

Protagonist and CIA veteran Harry Pappas has lost a son, an idealist who signed up to fight the war in Iraq after being horrified by the events of Sept. 11. After his son died in battle, Pappas started questioning U.S. motives for doing just about everything. What he finds is a growing mood of war-mongering that has very little to do with reality.

Take this conversation between two CIA operatives discussing an imminent confrontation with Iran, a face-off that seems to be based on very limited evidence of Iran’s potential to develop nuclear weapons:

“That’s insane,— said Harry. “What’s the rush? Why be in a hurry to make a mistake?—

“Because the president is determined to be firm. This problem isn’t going away. Leadership is about making the tough decisions.—

In addition to the somewhat unsavory reminders of a closed mindset, Ignatius does some other things very well. As the author of the best-selling thriller “Body of Lies,— he knows how to set up a feeling of suspense — Who will escape? Who is to be trusted and who is really a double agent? Will a young scientist who is dropping hints about Iran’s nuclear program be caught?

Ignatius also does a good job imagining the repressive regime that appears to govern Iran, dotted with cafes where patrons take care not to let their conversations be overheard and filled with citizens who know better than to read certain authors in public. He also uses details taken from stories he reported for the Post, such as a description of an old tuberculosis sanatorium north of Tehran that had been converted into a treatment center for AIDS. In fact, in 2006, Ignatius wrote a feature story for the Post about the doctor who runs the AIDS clinic, which the doctor described as “more enlightened— than what we have in this country.

Not every part of the book works quite so well, however. There is the usual tendency to fall into boilerplate spy/thriller cliché: the sexy and impossibly beautiful CIA agent who uses sex to have power over men; the hardened, chain-smoking old broad who knows everything; the bitter Brit who calls everyone “old chap—; the easily fooled Iranian guard who is wooed by being called “brother.— You get the picture.

Ignatius also asks us to believe that a CIA agent who goes rogue to prevent America from getting into another war without sufficient evidence would be able to do so secretly, even jetting back and forth between the U.S., Britain and the Middle East without, apparently, attracting much notice from the CIA, his wife or anyone else. Really? He also asks us to believe that a couple of his characters can zip off to the Inn at Little Washington on a day’s notice and have a cozy, private meal with no neighbors listening in. I don’t know what inn Ignatius is thinking of, but the one in Washington, Va., usually requires diners to make a reservation exactly one month before the dining date and the tables are within inches of each other.

But these are small quibbles. For the most part, “The Increment— delivers what it promises — a story to make the heart race, played out in a setting that makes the blood run cold.