How, after one of the most horrifically violent months in the history of Iraq, will Army Gen. David Petraeus make the political case — and, make no mistake, the likelihood at this point is that the top U.S. commander in Iraq will appear before Congress next week to deliver a politic rather than a military message — that the Bush administration’s “surge” is working?

All indications are that he will count on the continued compliance of a Congress that has established a remarkably consistent track record of failing to challenge even this administration’s most ambitious assaults on reality.

But, if advance reports regarding Petraeus’ scheduled truth-bending session prove accurate, the general may be asking too much of even the most credulous congressmen.

Petraeus is expected to tell the Congress — presumably with a straight face — that Iraq has seen a 75 percent drop in sectarian violence. The general’s aide’s in Baghdad are peddling numbers that suggest attacks motivated by religious and ethnic antipathy fell to 960 a week in August — down from 1,700 a week in June.

Petraeus is expected to claim, as well, that civilian casualties have dropped by 17 percent since before the surge.

That sounds like the right trend.

Unfortunately, it is based on the wrong numbers.

Petraeus and his aides have been caught cooking the books.

The Washington Post reports that serious analysts of the death and destruction data from Iraq “have looked at the full range of U.S. government statistics on violence (and) accuse the military of cherry-picking positive indicators and caution that the numbers — most of which are classified — are often confusing and contradictory. “

No less a watchdog than U.S. Comptroller General David Walker says, “Let’s just say that there are several different sources within the administration on violence, and those sources do not agree.”

Why don’t they agree? Because Petraeus the figures that is expected to peddle have been developed with the intent of creating a false impression about actual levels of violence in Iraq.

What’s the trick? Petraeus and his number crunchers are apparently determined to continue claiming that many of the most dramatic killings of recent months were not the result of “sectarian violence” but rather “criminal” murders. All indications are that these “criminal” incidents won’t be counted in the total figures presented to Congress as part of Petraeus’ assessment of the trends in Iraq.

Worse yet, Petraeus apparently intends to exclude information about the open warfare between rival Shiite militias in southern Iraq. Despite the fact that some of the worst fighting in Iraq is now between Shiite factions, the exclusion of such information creates a false impression. Yet, a spokesman for the Baghdad-based Multi-National Force-Iraq, has admitted that, “Given a lack of capability to accurately track Shiite-on-Shiite and Sunni-on-Sunni violence, except in certain instances, we do not track this data to any significant degree.”

Also excluded by Petraeus will be information about attacks by Sunni groups that have, for the moment at least, allied with U.S. forces.

What this adds up to is the simple reality that, if Petraeus uses the statistics he and his aides have been citing in the build-up to his appearance, the general will go before Congress with the intent of deceiving the elected representatives of the American people.

It is true, though sadly unlikely, that Petraeus could break pattern and speak truth about the burgeoning crisis over which he presides in Iraq. Perhaps he will decide that he cannot betray the truth — and with it the troops in his command, the people of Iraq and the promise of American military guided by principles rather than politics.

But if the general fails to speak that truth, then members of Congress have a responsibility to challenge the validity of the statements that are presented next week. It will fall to those members, Democrats and Republicans, liberals and conservatives, to clarify for the American people that — like George Bush and Dick Cheney — Petraeus is speaking not as a credible military commander, but as an advocate for the current administration’s political agenda of claiming that the “success” of the surge justifies an open-ended occupation of Iraq.

A failure on the part of all members of Congress to assure that the truth comes out — a truth that is readily available and that has already been bluntly stated by government and private intelligence analysts — would represent a collapse of the Constitutionally-defined separation of powers more serious even than the failures of the House and Senate to check and balance the Bush administration on the eve of this still-undeclared war.