"HEARTBURN" has been so waspified you'd think Nora Ephron had married Woodward instead of Bernstein. Mark Feldman becomes Mark Forman, and kreplaach becomes spaghetti carbonara.

But like the heroine herself says, the trouble with Washington is it's so goyish. At least, she said that in the book. In the movie, she's too goyish. And the novel, an acidic roman a clef by a woman wronged, becomes a tame domestic drama.

Ironically, the antacid was administered by a litigious Carl Bernstein who won a say in the script. In the film version, the rat Ephron so happily roasted becomes a likable cad. And the story becomes a tragi-comic chronicle of the storybook courtship and collapsed marriage of a couple of mismatched urban wordsmiths.

Meryl Streep is at her most accessible as New York food writer Rachel Samstat, who's heartbroken when she learns of her husband's affair with another woman. She's seven months pregnant and swollen as a gourd when she finds out about the tall, thin, other woman (a glimpse of Karen Akers). Whether we want to or not, Jack Nicholson makes us understand the scoundrel Mark, a moody Washington columnist with a roving eye. After their first baby girl arrives, he tires of peanut butter banality, seduced by Potomac fever.

The larger-than-life stars do squeeze into this small-scale soap opera without quite bursting the seams. They're nicely matched but hampered by a long, nuzzling preamble featuring the endearing details of their wedding and pre-marital woo. When the scope opens up and the focus comes clear, they couldn't be better -- they're every couple with dead dreams. But by then, the story has lost impact; better to have begun with the pain and flashed back on the joy.

Stockard Channing and Richard Masur co-star as the couple's best friends, providing shoulders to cry on and a lot of comic relief from the screenplay's relentless hominess -- Rachel shopping, cooking, mothering. Catherine O'Hara adds sparkle as a gossipy reporter, with Milos Forman in his acting debut as her Czech boyfriend. The elegant Akers, alas, is never seen again, and we don't even get the satisfaction of a good catfight.

Director Mike Nichols, who last collaborated with Streep and screenwriter Ephron on "Silkwood," misses many such opportunities. He seesaws from ridiculous to sublime, milking barren scenes for comedy one instant, finessing a ticklish scene the next. One touching segment sees Rachel seeking sympathy from her addlepated old dad (Steven Hill). "Men, I hate 'em," he consoles. She crumples and the baby wails in the other room.

Streep is trying her first comedy, right down to pie in Nicholson's face. Her timing isn't perfect but neither is Nichols' in her clumsy, climactic scene taken verbatim from the book. But other tidbits and comic dilemmas make a graceful transition along with the plot. What's missing is Ephron's talent for introspection, for laughing at herself.

Here, Ephron softpedals her rage, perhaps hamstrung by Bernstein's demands, or by Nichols' belief that audiences simply would not buy the book's lopsided scenario. What evolves is a more balanced portrait of a marriage, but an ambiguous artwork with no sense of moral outrage. Mark is a restless everyman and Rachel is a watermelon-shaped martyr who just doesn't fit his needs anymore. No one's to blame in our modern world. And that doesn't add up to double-digit "Heartburn," just a little belly-aching.

HEARTBURN (R) -- At area theaters.