UPDATE 1-U.S. screens 1.64 mln people at airports, highest since March 2020

(Adds more details, stock prices)

By David Shepardson

WASHINGTON, May 7 (Reuters) - The U.S. Transportation Security Administration (TSA) said it screened 1.64 million passengers on Thursday at U.S. airports, the highest number since March 2020, when the coronavirus pandemic slashed travel demand.

The number of U.S. air travelers is still about 35% lower than the same date in 2019, down nearly 1 million travelers, TSA said. U.S. airlines have been adding more flights, anticipating rising summer travel demand.

U.S. airline stocks rose Friday on optimism about travel demand, with United Airlines up 2.3%, American Airlines up 2% and Delta Air Lines up 2.3%.

This is the second new post March 2020 high set this week. TSA said it had screened nearly 1.63 million passengers on Sunday at U.S. airports. Thursday's figure was up about 17,000 over Sunday.

By comparison, just 190,000 people were screened at U.S. airports on the same day in May 2020. U.S. airlines have been adding more flights, anticipating rising summer travel demand.

Last month, United Airlines said it was adding more than 480 daily flights to its U.S. schedule in June to meet summer travel demand that is expected to rise as more people receive COVID-19 vaccines.

American Airlines said in April it expects to fly more than 90% of its domestic seat capacity compared with summer 2019 and 80% of its international seat capacity compared with 2019, and it will operate more than 150 new routes this summer.

Airlines are seeing an uptick in bookings as accelerated vaccination efforts encourage leisure travel with friends and family after months of pandemic-linked restrictions. (Reporting by David Shepardson; Editing by Toby Chopra and Marguerita Choy)