The announcement is likely to anger Beijing, which views Taiwan as part of its territory and has previously expressed "serious concerns" about the possible sale.
It coincides with other strains in US-China ties, particularly over trade.
Congress has been notified about the potential deal, which would include 108 M1A2T Abrams tanks, about 250 Stinger missiles, related equipment and support, according to the Defense Security Cooperation Agency (DSCA).
US lawmakers have 30 days to object to the sale but are unlikely to do so.
The proposed tank sale "will contribute to the modernization of the recipient's main battle tank fleet, enhancing its ability to meet current and future regional threats and to strengthen its homeland defense," DSCA said.
And the missiles would "support the foreign policy and national security of the United States by helping to improve the security and defensive capability of the recipient, an important force for political stability, military balance, and economic progress in the region," it said.
Neither would alter the "basic military balance in the region," according to DSCA.
Beijing registered its opposition to the possible sale earlier this month.
"We have repeatedly emphasized to the US to fully understand the extremely sensitive and damaging nature of their decision to sell arms to Taiwan, and abide by the One China principle," foreign ministry spokesman Geng Shuang said.
- Obsolete equipment -
Taiwan has been ruled separately since the end of a civil war in 1949, but China maintains it is a part of its territory to be retaken, by force if necessary.
China has significantly stepped up diplomatic and military pressure on Taipei since Beijing-sceptic president Tsai Ing-wen was elected in 2016.
It has staged military exercises near the island, and steadily reduced the already small number of nations that recognize Taiwan.
The United States switched diplomatic recognition from Taiwan to China in 1979, but Taipei has remained an important ally.
In recent years, Washington has been wary of completing big ticket arms deals with Taiwan, fearful of stoking China's anger.
But President Donald Trump -- whose administration is locked in a trade war with Beijing that has seen the two sides impose tariffs on hundreds of billions in two-way commerce -- has sought to strengthen ties with Taipei and appeared more willing to sell major weapon systems.
Taiwan acknowledged the US support for its defense systems in a statement released by its Foreign Ministry.
"Taiwan stands in the frontline of China's ambitious expansion and faced enormous threats and pressure from Beijing," the statement said.
"This arms sale of M1A2 tanks and various missiles will help greatly to increase our defensive capabilities."
Taiwan would be massively outgunned in terms of troop numbers and firepower in any war with China and needs to upgrade much of its equipment.
Its current tank force consists of around 1,000 CM 11 Brave Tiger and M60A3 tanks, technology that is increasingly obsolete.
Abrams tanks and anti-aircraft missiles that can be quickly moved by soldiers in the field would significantly increase Taiwan's ability to destroy Chinese armor and warplanes in the event of an invasion.