NEW YORK—A stock market gaining confidence in the nation’s financial system bolted higher Wednesday, propelling the Dow Jones industrials and Standard & Poor’s 500 index to their first four-day advance since last spring.

The market reversed losses from earlier in the session after President-elect Barack Obama pledged he would have a plan to deal with the nation’s economic crisis on his first day in office. After filling more spots to his economic team, Obama stated that “help is on the way.”

The major indexes built on their gains through the afternoon, but analysts caut...

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