John Adams was to the Continental Congress what George Washington was to the Continental Army: the indispensable man. He helped forge the United States, then became its first ambassador to England, first vice president and second president.

KENT EANES Paul Giamatti (left, as John Adams) and David Morse (as George Washtington) play the Founding Fathers on HBO's "John Adams."

He enjoyed the love of a beautiful and wise woman, the peerless Abigail Adams. His intimate circle included Washington, Franklin and Jefferson. When he died at the age of 90, the mourners included his son, President John Quincy Adams.

What an extraordinary American.

What a monumental disappointment.

That, at least, is the impression left by the first four hours of HBO's “John Adams,” an eight-hour-and-20-minute epic that premieres tonight at 8. The cable network withheld from reviewers the seven-part miniseries' final three episodes, but Paul Giamatti's nuanced performance is apt to become more, not less, dour. Episode Four ends before Adams' feud with Jefferson; his troubled presidency and doomed re-election campaign (Jefferson again!); and the deaths of his alcoholic son, Charles, only 30; daughter, Nabby, a cancer victim at 49; and beloved wife, taken by typhoid fever at 74.

DETAILS "John Adams" Seven-part miniseries on our second president. When: Parts 1 and 2 premiere tonight, 8-10:45 Where: HBO

Even before these tragedies and setbacks, “John Adams” is a study in tormented ambition. In a key scene, Ambassador Adams wins a postwar audience with King George III, the British monarch who had once threatened to execute Adams and his fellow American revolutionaries. The brief meeting, understandably tense and surprisingly tender, is a diplomatic coup.

But Adams makes the mistake of reading the next day's London newspapers.

“They accuse me of vanity!” he sulks to Abigail. “They always accuse me of vanity!”

They have reason. Giamatti's Adams is proud and unbending, passionate yet priggish, a loving father who is not above bullying his children. He is a great man haunted by petty fears, chief among them that his greatness will go unnoticed.

“John Adams” does not unearth the roots of these fears. The series begins abruptly in 1770, when Adams was already 34, married and an established lawyer. Over the objections of his firebrand cousin, Sam Adams (Danny Huston, the chief vampire in “30 Days of Night”), he agrees to defend the British soldiers accused of the incident known as the Boston Massacre.

HBO John Adams, brilliantly played by Paul Giamatti, was - and still is - often overshadowed by his fellow Founding Fathers, George Washington and Thomas Jefferson.

While most of the miniseries hews closely to its scrupulously accurate source, David McCullough's Pulitzer-winning biography, this segment is a notable exception. Adams stumbles upon the Boston Massacre's victims moments after the troops fired; tracks down reluctant witnesses; tricks a hostile witness into making a key admission; and defies a bloodthirsty Sam, glowering from the gallery. This isn't history; this is “Law & Order: Colonial Intent.”

These early scenes also fail Abigail Adams (Laura Linney), reducing this remarkable woman to Ye Olde Dutiful Wife, bestowing good counsel in private and fretful glances in public. “John Adams” is staid and narrow – the Continental Congress is a dreary gang of bewigged bores – until Adams leaves the colonies to seek French aid. His transatlantic voyage is suspenseful; his arrival in Paris provides the first overdue touches of comedy.

At a formal dinner, the proper Bostonian shrinks from his French companions, men and women caked in makeup, faces clown-white and lips cherry-red. An effeminate roue quizzes “Meestair Haddam” on the “arts of love.” Adams strains to acquit himself with dignity, but his fellow American envoy fears that the latter-day Puritan will never succeed in the court of King Louis XVI.

“You are a very good man, a very moral man, John Adams, but not a man for Paris,” remarks Benjamin Franklin (Tom Wilkinson). “Paris requires a certain amount of indecency in thought and action.”

Wilkinson, fresh from his Oscar-nominated turn in “Michael Clayton,” plays this Founding Father as a sly politician and relentless hedonist. He's a cross between Karl Rove and Hugh Hefner, playing chess in the bathtub with a randy crone, the wizened Madame Helvetius. Adams resents that this dirty old man is their mission's leader. Franklin responds by informing Congress that his Massachusetts colleague, “at some times and in some things, is quite out of his senses.”

There are times when “John Adams” could use more Franklinesque irreverence and less Adamsonian propriety. In the second episode, we see Abigail and several Adams children standing on a snowy hill over Boston harbor, watching British warships shell rebel strongholds. The scene is striking yet stately, removed from the action. Adams was a politician-diplomat, not a warrior, but it is difficult to sense what his family, literally standing above the fray, might gain or lose.

The diplomatic missions, too, are fuzzily described. We see Franklin in full oo-la-la mode and Adams, homesick and irritated by the languid French,screaming with frustration. We see Jefferson (Stephen Dillane) arrive in France and attempt to mediate the rift between his fellow Americans in Paris. But how these men wrested money and arms from France and then a treaty from England is never clear.

If the era's politics are often out of focus, “John Adams” sharply presents our Founding Fathers and Mothers as mere humans – geniuses, yes, but geniuses with foibles and failings. They did not, as is sometimes argued, think, speak and act with one voice, an Enlightenment version of “Star Trek's” Borg. Instead, they argued, sniped and even stooped to dirty tricks. (Here's hoping a later, unscreened episode shows Jefferson secretly orchestrating newspaper attacks on Adams when both were members of Washington's cabinet.)

They also loved. As the series proceeds, Giamatti and Linney delve deeper into John and Abigail's great affair. Reunited in Paris after the British surrender, John shepherds his wife through the American mission's palatial rooms. He is aloof and almost cold, until they gain the bedroom. There, he unbuttons her gloves, showering kisses on her hands.

Buttons and kisses fall elsewhere, and young viewers may see too much. But beyond Giamatti and Linney's full-blooded performances, “John Adams” soars when we see the messy, shocking, surprising details of this era: A Tory sympathizer is brutally tarred and feathered; the Adams children endure a bloody and controversial new medical procedure, chickenpox inoculations; John and Abigail are stunned to witness a hot air balloon rising into the French sky.

We also see, throughout, Adams wrestling his ambitions. This match is rigged; the great man is surrounded by greater men. Home from Europe before the first presidential election, John and Abigail dream big, but only within reason.

“You must at least be vice president,” Abigail counsels, aware that Washington is the natural choice for the top spot. “Anything less would be beneath you.”

Our second president lacked his predecessor's majesty and his successor's poetry. Our capital city is named for Washington, and his soaring monument commands the center of our National Mall, within site of the Jefferson Memorial.

No national monument honors Adams. Now, though, he is saluted by an HBO series that, like the man, is flawed but admirable.