Unnamed state department and Pentagon officials were quoted as saying the military assistance would provide $30bn in new US aid to Israel and $13bn to Egypt over 10 years.
The arms deals, said to be the largest negotiated by this administration, would include the sale of sophisticated weaponry.
"We're paying attention to the needs of our allies and what everyone in the region believes is a flexing of muscles by a more aggressive Iran"
Senior US administration official
Officials said the sales to Saudi Arabia were expected to include air-to-air missiles as well as joint direct attack munitions, which turn standard bombs into "smart" precision-guided bombs, the reports said.
The deals are designed to support US allies in the Middle East as a counterweight to regional power Iran.
The reports said the common goal of the military aid packages and arms sales is to strengthen pro-Western countries at a time when Iran seeks to extend its power in the region.
One official was quoted as saying: "This is a big development, because it's part of a larger regional strategy and the maintenance of a strong US presence in the region.
"We're paying attention to the needs of our allies and what everyone in the region believes is a flexing of muscles by a more aggressive Iran. One way to deal with that is to make our allies and friends strong."
Bearing on Iraq
The New York Times also reported that the timing of the plan was creating concern within Israel. Some US officials say the Saudi government is not helping the situation in Iraq, and is supporting Sunni fighters against the Shia leadership there.
Officials said such concerns had been sidestepped as the Bush administration was also offering massive military aid to Israel.
Administration officials remain concerned, however, that the package could draw opposition from some in congress who are critical of the Saudi government.
Assurances from the Saudis about being more supportive in Iraq were not sought by the administration as part of the deal.
The administration's plans will be announced on Monday before Condoleezza Rice, the secretary of state, and Robert Gates, the defence secretary, travel to the Middle East.
State Department and Pentagon officials had started briefing members of congress about their intentions over the past week, the newspapers also reported.