The delivery of four Lockheed Martin F-16 strike jets to Egypt has stirred congressional ire as Egypt's pro-democracy revolution hangs in the balance, with Islamists seeking to tighten their grip on power.

The jets, which reached Egypt Sunday, are the first of 20 Block 52 F-16s due to be delivered this year under a $1.3 billion a year U.S. military aid program signed by the regime of President Hosni Mubarak, a key U.S. ally who was swept from power in February 2011.

Amid a new wave of political upheaval, this time against Mubarak's Islamist successor, Mohamed Morsi, who's viewed with deep suspicion by the Americans, Republican lawmakers have sought to have the F-16 deliveries blocked.

"I think it's a blunder of the first proportion to send sophisticated weapons to a country that's allowed a mob to attack our embassy and to burn our flag," U.S. Sen. Rand Paul, R-Ky., said on the Senate floor last week.

The aircraft scheduled for delivery in 2013 are 16 F-16Cs and four F-16Ds. These make up a U.S. Foreign Military Sales program known as Peace Vector VII signed in December 2009 that will raise Egypt's inventory of the Lockheed Martin jets to 240.

The arms program is part of a major U.S. effort to modernize Egypt's armed forces and phase out Soviet-era weapons systems. It began after Egypt became the first Arab state to sign a peace treaty with Israel in 1979.

The United States viewed military investment in Egypt as a crucial element of its Middle East policy centered on Israel.

Mubarak was an avid champion of that strategy but his downfall after 40 years of dictatorial rule and the marginalization of Egypt's powerful generals military threatened to unravel U.S. policy, and undermine the peace treaty with Israel.

These threats intensified when the Muslim Brotherhood took power in parliamentary elections in 2012.

Morsi, an Islamist elected in June, is grappling with a new uprising triggered by his efforts to monopolize power in his own hands. More than 100 people have been killed in street battles since Jan. 26.

Paul proposed a bill in the U.S. Senate prohibiting the sale of F-16s, M1A1 Abrams tanks built by General Dynamics Land Systems, and other advanced systems to Egypt while the Muslim Brotherhood is in power.

Egypt is also scheduled to get 200 Abrams this year, bolstering its inventory of more than 1,000 M1A1s, some built under license in Egypt.

"I find it objectionable to send weapons, F-16s and tanks, to a country that allowed a mob chanting 'death to America' to threaten out American diplomats," Paul said.

An arms ban would hit the U.S. defense industry hard at a time of some $600 billion in defense cuts over the next few years starting in March.

Exports of weapons systems and other equipment have become crucial in keeping assembly lines running.

Lockheed Martin, the leading U.S. defense contractor, has said its sales would decline in the next fiscal year even without the across-the-board U.S. cuts, known as sequestration.

Lockheed, Northrop Grumman, General Dynamics and other defense majors have reported strong performances in 2012, despite the looming threat they face.

But if military exports are hit, the long-term prospects are bleaker.

Sen. James Inhofe, R-Okla., the new ranking member on the Senate Armed Services Committee, introduced similar legislation to Paul's.

But he acknowledged that an outright ban on arms sales to Egypt, the most populous Arab state which fought four wars with Israel since 1948 and lost all of them, would cause serious harm to the United States.

Inhofe estimated a total ban would cost the U.S. defense industry $2.2 billion and diminish U.S. leverage over Egypt.

Instead, he suggested the United States suspend military sales to Egypt, which are vital to the country's upgrading of its armed forces, unless U.S. President Barack Obama certifies Egypt is committed to observing the peace treaty with Israel.

U.S. Rep. Louie Gohmert, R-Texas, declared the arms deliveries "insane" Jan. 24, and blasted the Obama administration for sending advanced weaponry "to a leader whose only two enemies, he said in the past, are Israel and the United States."