If in its final hours Syria's crumbling government unleashes a chemical barrage – and some analysts certainly think that's possible – the regime will probably rely on an arsenal of gas- or nerve agent-tipped ballistic missiles purchased from Iran and North Korea.

But precisely how many and what mix of missiles President Bashar Al Assad controls, and therefore how deadly a chemical strike might be, both remain unclear. Equally unclear is how far the world should go to defend against such a strike.

Chances are, Syria possesses at least three types of ballistic missile that can be fitted with chemical warheads, according to Dr. Jeffrey Lewis from the James Martin Center for Nonproliferation Studies in California. These include Scuds and SS-21s acquired from North Korea and, less clearly, Fateh 110s transferred from Iran.

The Fateh 110s and SS-21s, both around 20 feet long, can reach just 50 and 120 miles, respectively. The Scuds, at 35 feet long, have a longer range: up to 400 miles. All the missiles are mobile – that is, they're carried and launched by wheeled or tracked vehicles. The Scud's so-called Transporter Erector Launcher is a heavy-duty offroad truck the size of a tractor trailer.

They're all also unguided, with abysmal accuracy – 200 feet at best, in the Scud's case. That means it can takes a lot of missiles to hit one target. According to various sources, Syria's stockpile could include between 100 and 300 Scuds, maybe 200 SS-21s and probably no more than 50 Fatehs.

The Scuds and SS-21s have been widely reported and even glimpsed in recent satellite imagery and in the video above, shot in June by the Free Syrian Army. These two missile types have guest-starred in scores of conflicts since the Cold War. Most recently, Iraq lobbed Scuds at coalition troops in 1991 and 2003. Russia fired SS-21s at Georgian forces in 2009.

But the Fatehs are "something no one talks about," Lewis, who also blogs at Arms Control Wonk, tells Danger Room. "That boggles my mind." The Fatehs are just part of a growing portfolio of Iranian-designed missiles and rockets meant mostly for domestic use in Iran's escalating standoff with most of the rest of the world and, to a lesser extent, for export.

One reason could be that the Fatehs arrived in Syria in just the last couple years, when Tehran took what Lewis calls the "unprecedented" step of transferring the missiles to Damascus – a move confirmed in a 2009 U.S. diplomatic cable released last year by Wikileaks. There were reports that Damascus passed the Fatehs on to Hezbollah, although Lewis says he's skeptical this has happened.

By contrast, Assad's regime has possessed Scuds and SS-21s for decades. The older missiles, originally Soviet in design, were practically staples of Third World dictatorships during the Cold War.

Though the oldest, the long-range Scuds "are clearly the big thing," Lewis says. Not only could these missiles strike rebel targets inside Syria, they've got the legs to target Syria's neighbors, including all of Israel. Saddam Hussein fired more than 40 Scuds with conventional warheads at Israel and Kuwait in 1991, killing one Israeli, one Saudi and 28 Americans from a Pennsylvania Army National Guard unit.

But a Syrian barrage is contingent on the missiles, some of which could be 20 years old, being in shape to fly. "They [missiles] don't take care of themselves," Lewis points out, "so we often see low rates of readiness in Third Word ballistic missile forces."

"Undoubtedly some are in working condition," Lewis cautions. "The Libyans took terrible care of their Scuds and were still able fire a few off towards the end."

If Syria does pop off some chemical-tipped Scuds, Israel should be able to defend itself with anti-missile systems including Patriot and Arrow interceptors. U.S.-manned Patriots hit several Iraq Scuds fired at Israel in 1991. Blowing up an incoming chemical warhead would still release some of the deadly agent, but the Pentagon estimated an intercept would "reduce the area of contamination significantly."

Short of a full-scale intervention, however, there's not much the world can do to defend the rebels and Syrian civilians against Assad's chemical-tipped missiles. Even a strictly aerial campaign might not work: Iraqi Scuds managed to hide from U.S. warplanes in 1991 and again in 2003. "What you would have to do is have people on ground engaging in a Scud hunt," Lewis says. At the very least, that means large numbers of Special Operations Forces plus the troops to support them.

The question is, is the possible threat from Syria's potentially chemical-tipped missiles worth the likely high cost of another U.S.-led war in the Middle East?