"We are in the final stages of a series of deals," the official was quoted as saying by Reuters on Friday, a week before Trump visits the oil-rich kingdom on his first foreign trip.
The deals exceed $100 billion at this stage and might be increased to $300 billion over a 10-year period, the official noted.
According to the unnamed official, the White House is aiming to help strengthen Saudi Arabia's armed forces while making sure that Israel, America's main Middle East ally, maintains its qualitative military edge in the region.
Trump has decided to visit Saudi Arabia before heading to Israel on his maiden international trip, a move that underscores the kingdom's significance in his foreign policy.
The American head of state would also offer the Saudis an $11.5 billion deal for four multi-mission warships and technical support. The US State Department approved the deal in 2015, however, it never went through because of disagreements on both sides.
The warships belong to the US Navy's Littoral Combat Ship class, which has been regarded by Pentagon officials as some of the most problematic and least equipped units operated by the force.
Saudi Arabia's Foreign Minister Adel al-Jubeir said earlier this month that Trump had taken steps in the congressional notification process for the sale of armor-piercing Penetrator Warheads and precision-guided Paveway missiles to the kingdom.
The US has long been providing intelligence and arms support to Saudi Arabia in its two-year-long aggression against Yemen.
Washington has been under pressure to stop selling Riyadh new weapons.
However, US Defense Secretary James Mattis said during his last month trip to Saudi Arabia that the new US administration would do its best to "see a strong Saudi Arabia."
The deals seem to be part of Trump's plans to boost manufacturing jobs in the US, a pledge he made during his election campaign.