The Syrian bloodbath has taken almost 20,000 lives over nearly 17 months and driven hundreds of thousands from their homes — but it won’t go on forever.

The question is: When will the fight between the rebels and the Bashar al-Assad regime reach the tipping point, pushing the civil war in one direction or the other?

It could come at any time, but will likely be based on a couple of factors.

First, toss out the notion of a UN-sponsored (or other) peace plan allowing Assad to quietly hit the bricks in favor of elections. Both sides are too determined to win to agree to any diplomatic deal.

It’s the level of outside assistance to the regime or the rebels that will make the difference in the battle for Syria. Up to this point, interested parties have played a low-key role in the uprising, but that could be changing.

The make-or-break help could come in the form of organizing the opposition politically — not to mention militarily. The anti-regime politicians and fighters are divided now along a number of fault lines, severely limiting their effectiveness.

Gulf states such as Saudi Arabia and Qatar are reportedly funneling money through Turkey to rebel groups, providing the means to buy arms and pay foreign fighters — and boosting the odds that these factions will come out on top should the regime fall.

News reports say the rebels may now have some man-portable surface-to-air missiles, which could be used against regime helicopter gunships or transport aircraft that move troops from hot spot to hot spot. (Of course, there’s no telling how long it will take the rebels to learn to use them effectively.)

The Saudis, Qataris and others have a keen interest in replacing the crowd running the show in Damascus. Not only would they knock off Iran’s most important ally, but they might also be able to put their team in charge.

Tehran isn’t likely to stand idly by, considering its interest in preserving its pals’ place in Damascus. Losing Syria would mean the end of an ally and the loss of the main conduit to Hezbollah in Lebanon — not to mention a major setback to Iran’s efforts to dominate a swath of the Middle East.

Reports indicate that Syrian and Iranian officials are consulting regularly on the situation; Tehran is believed to be supplying Revolutionary Guard and Qods Force advisers as well as weapons to Assad’s forces. Hezbollah may also be operating in Syria.

Another key factor will be Assad-regime and loyalist defections. Some senior military and government figures have already switched, but more important will be changes of allegiance by military units like the Republican Guard or among the Syrian army of nearly 300,000 troops.

Assad’s forces could boost the desertion rate by vastly increasing the bloodshed against innocents, losing expanses of territory or using Syria’s vast chemical-weapons arsenal against the people, which is possible, but unlikely until things turn more dire for the regime.

Unfortunately, as it looks now, it doesn’t appear that we — or the West — will be a big player in the struggle for Syria, despite breaking news of possible new, non-lethal US support to the rebels. That’s really troubling, since Syria is of strategic importance to US and Western interests.

Others — notably the Turks, Saudis and Qataris — are filling the void left open by absent US leadership.

Without big efforts to shape Syria’s outcome, we’re likely to be dealing with a really hacked-off Assad regime, a less-than-friendly Islamist government or complete chaos, where extremists could thrive — in a country with the Middle East’s largest chemical-weapons arsenal.

None is an outcome we should be looking forward to.

Peter Brookes is a Heritage Foundation senior fellow and a former deputy assistant secretary of defense.