* Demand increased slowly during summer - SAS

* On business travel, we have to "wait and see"

* Airline reports $157 million quarterly loss (Adds CEO comment)

By Niklas Pollard and Anna Ringstrom

STOCKHOLM, Sept 1 (Reuters) - Scandinavian carrier SAS said it was seeing some signs of recovery in air travel as it reported a narrowing quarterly loss, but its new CEO warned it would take years for demand to return to pre-pandemic levels.

The airline, part-owned by the governments of Sweden and Denmark, said it had been encouraged by a gradual increase in demand during the summer holiday season as vaccination drives gathered pace around the world.

Yet Chief Executive Anko van der Werff said that while he expected continued demand for leisure flights, the shape of business travel was more uncertain.

"September, October and November are really strong corporate months typically. Now it's Sept. 1 and people are booking very late, very close to departure so we just have to wait and see a bit longer," he told Reuters in an interview.

He declined to give a specific prediction for when overall demand might fully recover from the COVID-19 crisis, though added: "2022 will be better than 2021, but it is in my view going to take years before you are back to 2019 levels."

That was a far more pessimistic outlook than SAS gave in December, when it said it expected demand in 2022 to reach levels "at least comparable" to those before the pandemic.

The CEO was speaking after his airline reported losses before tax of 1.36 billion Swedish crowns ($157 million) in its fiscal third quarter running from May through July, versus a 2.08 billion loss in the same period a year earlier.

Van der Werff, previously the head of Colombia-based Avianca , the first major carrier to file for bankruptcy due to the pandemic, took the SAS helm in July after his predecessor unexpectedly announced his resignation.

"We were the first industry to get really hit by the pandemic and we will be the last industry out. That's how I look at it in other parts of the world, and it's definitely also how I look upon it for Europe and for SAS," he said.

"We really have to make sure that we are flexible, because we don't know how long this will take, and that we remain very competitive."

($1 = 8.6386 Swedish crowns) (Reporting by Niklas Pollard and Anna ringstrom; Editing by Simon Johnson and Pravin Char)