Decisive moves by the head of the European Central Bank sent the benchmark American stock index to a four-year high and fueled hopes that the foundation for a more lasting solution to the European debt crisis may be taking shape.


The Standard & Poor’s 500-stock index jumped 2 percent by the close to its highest level since January 2008. The Dow Jones industrial average added about 244 points, or 1.9 percent. And the Nasdaq composite index gained 2.2 percent for its highest close since 2000.


The markets have greeted several previous efforts to solve Europe’s economic woes with euphoria, only to be quickly deflated. While investors were bracing for the latest plan to run into problems, there were numerous signals that this plan may have a staying power.


Stock indicators were moving up even before the central bank announcement because of two promising new data points on the United States employment picture. The number of people filing for unemployment benefits last week fell 12,000 from the week before, and the payroll company ADP said private companies added 201,000 jobs in August.


While the European Central Bank program was largely what investors had been expecting, it helped push stocks up further.


Quincy Krosby, a market strategist at Prudential Financial, said that the central bank’s commitment to buying sovereign bonds eases lingering concerns about an immediate crisis in Europe among American investors.


“The endemic problems in the euro zone have held U.S. markets hostage,” Ms. Krosby said. “Perhaps for the short term, the panic doesn’t have to set in every time there is a bond sale.”


In Europe, stock market indexes closed with gains of more than 2 percent, with Spanish and Italian stocks up more than 4 percent. The DAX in Frankfurt added 2.9 percent. The FTSE 100 in London gained 2.1 percent.


Long-term European bonds also rose, with their yields falling sharply. The Spanish 10-year bond fell to 5.959 percent.


To the degree that the bond-buying takes pressure off Europe, it will allow investors to shift their attention to the economy in the United States and the monthly jobs report that is due out on Friday.


That, in turn, could influence the decisions made at next week’s meeting of the Federal Reserve’s Open Market Committee, which has been contemplating providing more monetary stimulus for the economy.