He said: "There are political questions in the US, always, involving any arms sales to Arab countries because of the very strong support in the US congress for Israel."
"The US congress needs to approve this arms deal - that's US law."
The sale appeared to be part of Bush's effort to persuade Saudi Arabia to help contain Iran and offset what he has branded a danger to the oil-rich region and to the world's security.
Ratcheting up the rhetoric, Bush declared in a speech in Abu Dhabi earlier this week that Iran was "the world's leading state sponsor of terror".
Tehran denounced Bush's comments as "words without value".
During his visit to Saudi Arabia, his first visit to the oil-rich US ally, Bush hopes to rally support for his campaign to isolate Iran.
His administration, which has also announced a $30bn military aid pact with Israel, has argued the deal with the Saudis is needed to counter what it claims is a "major security threat" from Iran.
While Sunni-ruled Saudi Arabia has voiced concern over the rise of Shia Iran, it is opposed to another war after the 2003 US-led invasion of Iraq that has strengthened the government in Tehran.