If the Americans finally unleash military strikes against Syria that end up hammering Bashar Assad's forces to help the divided rebels, one of the key targets will be the Syrian air force.

It's arguably one of the Damascus regime's most potent weapons against which the rebels have few defenses and which has hit them hard time after time.

That has allowed Assad's forces, reinforced by Lebanon's Hezbollah and Hezbollah-trained Shiite veterans from Iraq, to blunt rebel offensives in a 2 1/2-year-old conflict that has largely stalemated.

It has becoming increasingly clear in recent months that the regime, aided by Russian weapons, has the capability to ride out the level of combat that characterizes the conflict these days, while the rebels do not have the strength -- or the unity -- to overcome the regime without a significant increase in external support, particularly surface-to-air missiles.

Hitting the regime's major airbases could fall in with the wider intervention that U.S. President Barack Obama now seems to favor, rather than restricting U.S. action to attacking chemical weapons-related targets with Tomahawk cruise missiles in retaliation for the Aug. 21 nerve gas attack that Washington says killed nearly 1,500 civilians on the outskirts of Damascus.

"Most importantly, the intervention should focus on weakening the regime's most potent strategic advantage: its air power," observed Lebanese military analyst Hussein Ibish.

"Above all, the systematic destruction of air bases and major landing fields under the control of the regime would dramatically shift the ability of Iran and Russia to supply men and materiel to the Damascus dictatorship."

Providing enough Syrian combat jets and helicopters are destroyed by U.S missiles and even airstrikes, this would significantly counter a sharp increase in air operations by the regime over recent weeks -- 500 missions in May, close to 600 in June.

The main problem for U.S. pilots would be Syria's dense 54,000-man air-defense system, equipped with effective Russian missile systems and radars.

This network is far more powerful and better prepared than the Libyan defenses that NATO airstrikes swiftly neutralized in the first few days of the campaign against Moammar Gadhafi in early 2011.

The risks are different too. Assad's Syria is not a friendless pariah, as Libya was. Russia and Iran are backing Damascus.

At least four relatively small airstrikes, all unacknowledged, against Syrian targets have been carried out this year, undoubtedly by the Israelis, without drawing any Syrian fire.

It's not clear why, but the Syrians probably didn't want to get into a shooting war with the Israeli air force.

In their last major engagement in the opening days of Israel's 1982 invasion of Lebanon, the Israelis shot down some 90 Soviet-supplied Syrian jets, a large chunk of Damascus' fighter force at the time, and destroyed 19 surface-to-air missile batteries for no losses.

If Obama does eventually decide to unleash a broadside of airstrikes, sustained for several days at least, against key Syrian targets, one of the first objectives will be to hammer Assad's air defenses in attacks launched from Turkey, Jordan and possible even Saudi Arabia, as well as navy carriers in the Mediterranean and Red Seas.

Meantime, the Syrian air force's increased tempo of operations has taken a toll, primarily through wear and tear, the result of poor maintenance, rather than through combat losses.

The rebels have shot down only a few aircraft since the war began in March 2011.

Most were downed in prepared ambushes in which the rebels set up "flak traps," clusters of heavy machineguns along the flight paths used by aircraft landing at their bases or by luring them into low-level attacks on strengthened rebel positions.

Some aircraft have been destroyed on the ground when the rebels overran regime air bases.

All told, according to rebel claims and Western estimates, Syrian losses, mainly due to attrition, accidents and aircrews' lack of training in counter-insurgency tactics, would appear to have been heavy, despite the rebels' lack of firepower against the aerial threat.

In July, Western experts estimated of the 370 operational fixed wing aircraft, mainly MiG-23s and 25s and Sukhoi Su-22s, the Syrian air force had in March 2011, half were destroyed or out of action, as were around half of its 360 helicopters.

But, for the rebels on the ground, that was still bad news.