Boston — The inflation rate is plunging far faster than most economists would have guessed last spring.
''The CPI is behaving better than almost any economist had expected,'' notes Robert J. Eggert, who keeps track of the forecasts of more than 40 top business economists in his letter, Blue Chip Economic Indicators.
Moreover, a high level of pessimism for the future of inflation is giving way to much more optimism.
February's consumer price index (CPI) confirms this shift. Cheaper gasoline and less expensive new cars helped hold the CPI to a monthly increase of 0.2 percent. That amounts to 3 percent when seasonally adjusted and compounded at an annual rate.
Since October, the CPI has risen at a 4.5 percent annual rate. And, using a statistical system designed to smooth out monthly variations and determine an ''underlying rate,'' Dr. Geoffrey H. Moore, director of the Center for International Business Cycle Research at Rutgers University in New Jersey, puts the current annual inflation rate at 6.7 percent.
All these numbers show rapid progress in reducing inflation. The news apparently cheered stock market investors. Prices were rising and volume reached a record level on the New York Stock Exchange in the first hour of trading Tuesday, March 23.
Last June, the Blue Chip consensus expected the inflation rate this year to decline from 8.7 percent in the current quarter to 8.2 percent in the last three months of the year. Earlier this month, the same group anticipated the CPI to rise at a 5.6 percent annual rate this quarter and increase to 6.8 percent by the final quarter.
However, Mr. Eggert says he expects this group of economists to drop their CPI forecast rates when surveyed early in April. ''The trend is clearly favorable,'' he says.
Dr. Moore, regarded as one of the world's top experts on the business cycle and a former director of the Bureau of Labor Statistics (which compiles the CPI) , points out that the current inflation rate - by his 12-month averaging technique - now is running at less than half the 15 percent rate the same conservative method yielded in 1980.
Further, Moore identifies several indicators that he says point to even lower inflation:
* Industrial materials prices have continued to decline.
''These prices are very sensitive to demand and supply pressures and are a good advance warning,'' he says.
* The employment ratio is down. This is the ratio of those employed to the total population aged 16 and over. The ratio was 57.3 percent in February, down from a cyclical peak of 59 percent last May. Over the long term, the employment ratio has risen as a higher proportion of women have entered the labor force. But the recent decline puts pressure on wages, which are a key element in costs and eventually prices. Dr. Moore considers this ratio as a better indicator of wage pressures than the unemployment level.
* Wage increases have dropped, both among unionized and nonunionized workers. When he was director of the Bureau of Labor Statistics about a decade ago, Moore introduced an employment cost index that is calculated at the end of each quarter. It was rising at an annual rate of 11.4 percent in March 1981 and at an 8.7 percent rate in December 1981.
Moore figures the recent rash of contract concessions by unions in high-wage industries facing deregulation or foreign competition should enforce this trend. Workers in the auto, rubber, steel, railroad, trucking, and airline industries have given up benefits.
Looking at the newly announced agreement between General Motors and the United Auto Workers union, Dr. Moore roughly calculated the wage and benefit increase at a 6.5 percent annual increase over the next 2.5 years. ''That is a far cry from the 10 percent or more wage increases that have been pretty common in recent years,'' he says.
* The growth of debt by business, consumers, and the federal government has fallen. The annual debt growth rate was 7.8 percent in December, down from about 9 percent in mid-1981. Since debt is used to buy goods and services, the decline in the growth rate for debt - especially by consumers and business - is a ''negative kind of pressure'' on prices, says Moore.
Another indicator of future prices, favored by so-called monetarist economists, is past growth in the money supply. Monetarists hold that the current level of inflation reflects the growth of the nation's money supply about two years ago. So, since the money supply growth rate started to decline about two years ago, inflation should continue downward.