By Lewis Krauskopf, Devik Jain and Anisha Sircar

June 21 (Reuters) - Wall Street's major indexes jumped on Tuesday as investors scooped up shares of megacap growth and energy companies after the stock market swooned last week on worries over a global economic downturn.

All 11 major S&P 500 sectors gained, as stocks rebounded broadly after the benchmark index last week logged its biggest weekly percentage decline since March 2020.

Investors are trying to assess how far stocks can fall as they weigh risks to the economy with the Federal Reserve taking aggressive measures to try to tamp down surging inflation. The S&P 500 earlier this month fell over 20% from its January all-time high, confirming the common definition of a bear market.

"Do I think we have hit bottom? No. I think we are going to see more volatility, I think the bottoming process will likely take some time," said Kristina Hooper, chief global market strategist at Invesco.

"But I do think it is a good sign to see investor interest."

According to preliminary data, the S&P 500 gained 90.05 points, or 2.45%, to end at 3,764.89 points, while the Nasdaq Composite gained 269.78 points, or 2.50%, to 11,068.13. The Dow Jones Industrial Average rose 654.10 points, Office 2021 or 2.19%, to 30,542.88.

The energy sector, the top-gaining S&P 500 sector this year, surged after tumbling last week.

Megacap stocks Apple Inc, Tesla Inc and Microsoft Corp all rose solidly to give big individual boosts to the S&P 500.

The Fed last week approved its largest interest rate increase in more than a quarter of a century to stem a surge in inflation.

Investors are pivoting to Fed Chair Jerome Powell's testimony to the U.S.

Senate Banking Committee on Wednesday for clues on future interest rate hikes and his latest views on the economy.

Investors are "trying to read the tea leaves to see how aggressive the Fed is going to get," said Chuck Carlson, chief executive officer at Horizon Investment Services in Hammond, Indiana.
"That's a hard question to answer right now because they are going to see what happens to the inflation story."

Meanwhile, Goldman Sachs now expects a 30% chance of the U.S. economy tipping into recession over the next year, up from its previous forecast of 15%.

In company news, Kellogg Co shares rose after the breakfast cereal maker said it was splitting into three companies.

Spirit Airlines shares jumped after JetBlue Airways said on Monday it sweetened its bid to convince the ultra-low cost carrier to accept its offer over rival Frontier Airlines' proposal.

(Reporting by Lewis Krauskopf in New York, Devik Jain and Anisha Sircar in Bengaluru; Editing by Sriraj Kalluvila, Arun Koyyur and Richard Chang)