The Israeli air force's lack of the systems is widely seen as a major impediment to Netanyahu ordering airstrikes aimed at slowing the Islamic Republic's nuclear program, which Netanyahu sees as an existential threat to his tiny country.
The Israeli request isn't new but the added urgency of Netanyahu's request during his Monday meeting with Obama underlined the do-or-die emphasis the hawkish Israeli leader places on eliminating the Iranian nuclear threat.
The Obama administration secretly supplied Israel with 55 of the 5,000-pound GBU-28s in 2009 but has rebuffed requests for more, apparently for fear it would encourage Israel to act unilaterally against Iran and trigger a regional war.
The Haaretz daily reported Obama has instructed U.S Defense Secretary Leon Panetta "to work directly with (Israeli) Defense Minister Ehud Barak on the matter, indicating the U.S. administration is inclined to look favorably upon the request as soon as possible."
Many military analysts say any Israeli attack will concentrate on hitting four key Iranian nuclear facilities -- the uranium-enrichment plants at Natanz and Fordow, the heavy-water reactor outside Arak, and the uranium conversion facility near Isfahan.
The Israeli air force has three possible routes to those targets -- north over Turkey, south through Saudi Arabian airspace or the central path over Jordan and Iraq.
Turkey is out following Ankara's May 2010 rupture of its longstanding alliance with Israel.
Saudi Arabia, Iran's archrival in the region, would likely privately applaud any Israeli operation to set back Iran's supposed drive to acquire nuclear weapons but it would probably stop short of opening up its air space to Israel's strike jets. However, some Israelis suspect Riyadh would turn a blind eye and feign ignorance.
U.S. defense analysts say the Jordan-Iraq route would be preferable, since Iraq has no air defenses to speak of after U.S. forces completed their withdrawal in December.
This is where the Israeli air force's lack of refueling aircraft becomes a crucial factor. The distance to target and back via the Iraq route is roughly 2,450 miles.
To effectively clobber the Iranian targets the Israelis would need to employ at least 100 of their strategic strike aircraft. These currently comprise 101 U.S.-built F-16I Sufas and 25 F-15I Ra'ams customized for the Israelis.
The F-15I, for instance, has a combat radius of 2,780 miles but with a full load of bombs and missiles these jets would probably need two in-flight refuelings during the mission.
Israel's capability in this regard isn't enough to cope with 100-plus strike jets to and from targets in Iran.
In recent years the Israelis have quietly acquired seven Boeing KC-707 tanker aircraft from the United States, along with at least five Lockheed C-130 transport jets that have been converted to the tanker role.
"Theoretically," said U.S. military analyst David Isenberg of the Cato Institute, "the Israelis could do this -- but at great risk of failure.
"If they decided to attack Natanz, they would have to inflict sufficient damage the first time -- they probably would not be able to mount follow-on strikes at other facilities."
The Israelis, U.S. officials say, have accepted their limited options and that, unlike the United States, they don't have the firepower to deliver a knockout blow to Iran's nuclear project, only set it back by a year or two.
All key sites are protected by modern Russian air-defense systems, so the Israelis would also probably need electronic warfare aircraft to blind Iran's defenses, as they did in the September 2007 strike that destroyed a North Korean-built nuclear reactor in eastern Syria.
Besides, the Iranians have reportedly been dispersing their nuclear facilities and burying them deep underground to protect them from bomb and missile attacks.
So the Israeli air force will need a lot of GBU-28s to get the job done.
In recent days, an added wrinkle has reportedly emerged.
Israel's Debka Web site, believed to be closely associated with Israeli intelligence, claims Russia has upgraded an electronic surveillance station south of Damascus tailored to extend Tehran's early warning system of an Israeli or U.S. attack from the Mediterranean.
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