U.S. stock index futures soared on Monday, and the S&P 500 could open 4 percent higher, after global leaders agreed to a $1 trillion emergency rescue package that sent the euro and European stocks surging.

The package pledged 500 billion euros ($670 billion) in loans and loan guarantees to euro-zone countries, plus about 250 billion euros from the International Monetary Fund. The package is on the same scale as the $700 billion bailout launched by the United States to stave off the credit crisis.

Also, the U.S. Federal Reserve reopened currency swap lines with several central banks in hopes of assuring markets of dollar liquidity, and the European Central Bank said it would buy government debt to steady investor nerves. A number of European central banks said they had already started.

S&P 500 futures rose 52.3 points and were above fair value, a formula that evaluates pricing by taking into account interest rates, dividends and time to expiration on the contract. Dow Jones industrial average futures shot up 400 points, and Nasdaq 100 futures gained 81.25 points.

In Europe, the pan-European FTSEurofirst 300 <.FTEU3> index of top shares advanced 6.5 percent, rebounding from its biggest weekly drop in nearly 18 months.

The heads of leading U.S. stock market operators were called to Washington for an emergency meeting on Monday to address whether they needed to add levers to their trading systems to halt sudden plunges in individual stocks, according to a source.

The meeting comes on the heels of last week's dramatic intraday plunge in U.S. markets that has continued to perplex investors and regulators.

In equities news, Boeing Co is on track to deliver its first 787 Dreamliner, which will compete with Airbus's A380 jet, a Boeing official said Saturday.

Stocks turned negative for the year on Friday on fears of another credit crisis stemming from Greece's souring finances and lingering questions about what triggered last week's sudden plunge.

(Reporting by Leah Schnurr; editing by Jeffrey Benkoe)