Economists at the Fed aren't obsessed with short-term pocketbook issues like high oil prices -- and not just because many of them commute to work in Washington on the Metro. Rather, they focus on long-term economywide issues.

"You want to make sure that short-term monetary policy isn't responding to a phenomenon that is just going to go away in a few months, or even a year," said Stephen G. Cecchetti, economics professor at Brandeis University. "A change in an interest rate today will have an effect on inflation one to two years from today." We would not have wanted the Fed to act as if the post-Katrina spike in gasoline prices were permanent, he noted.

What's more, the Fed tends to focus on things that it can control. Not even a Fed chairman as powerful as Alan Greenspan can affect the price of oil by manipulating interest rates. "There's nothing the central bank can do about that, unless it figures out how to produce more oil," said Michael F. Bryan, vice president and economist at the Federal Reserve Bank of Cleveland.

But the Fed can control the amount of money circulating in the economy relative to the quantity of goods available. "So it tries to find the inflation signal common to all prices throughout the economy," Mr. Bryan said.

Thus considered, the core C.P.I. may be the best tool the Fed has to monitor long-term changes in prices.

Still, economists see two good reasons not to ignore the headline number today. First, inflation in a crucial category like energy can worm its way into the entire system. "If high energy costs persist, and if they continue to rise, they may ultimately seep into the core," Professor Owen said. The second reason has less to do with hard economic realities than with softer perceptions. The cost of gasoline is the economy's most visible price. People see it every day even if they don't buy gas every day, said Matthew Martin, senior economist at Economy.com. And most people buy food every week.

"If prices for those two things go up quickly, consumers will form the impression that inflation is high," he said. "And if consumers begin to expect more inflation, they might be more tolerant of price increases."

If that happens, the headline C.P.I. number could dominate the headlines.

ECONOMIC VIEW Daniel Gross writes the "Moneybox" column for Slate.com.