Imported products cost American consumers 9.6 percent more last year than in 1986 as the dollar decreased in value against other major currencies, the Labor Department reported yesterday.

The figures for the year showed that prices of all imports increased 14.8 percent, but import prices went up less -- 9.6 percent -- when volatile petroleum prices were removed.

But the end-of-year report on U.S. import and export prices showed that foreign suppliers cut prices in their own currencies to help maintain their market share in the United States.

The information, compiled by the Labor Department's Bureau of Labor Statistics, shows how the Reagan administration's policy of letting the dollar's value fall relative to currencies of major trading partners has succeeded in making imports more expensive, and therefore less competitive here.

But imports, as measured by the closely watched monthly merchandise trade figures, have remained high, partly because foreigner suppliers have not increased prices as much as the 50 percent depreciation of the dollar and partly because higher prices mask a cut in the volume of imports.

The monthly trade figures released last week showed U.S. consumers bought $387.1 billion in imports during the first 11 months of last year, $36.4 billion more than during the same period in 1986.

But U.S. Trade Representative Clayton K. Yeutter has compiled figures using constant dollars amounts that show imports have increased far less, 3.1 percent, from the third quarter of 1986 to the third quarter of 1987 when price increases caused by currency fluctuations are removed.

In a statement issued yesterday based on unpublished figures from the Commerce Department, Yeutter said the trade deficit in volume terms "peaked in the third quarter of 1986 and has declined ever since.

"Unfortunately, these improvements are often masked by changes in exchange rates, which raise the the price of imports," Yeutter said.

The Labor Department figures measure the currency changes.

"By comparison, nonenergy import prices rose 8.4 percent in 1986, following three years of relatively little movement," said Bill Alterman, an analyst at the Bureau of Labor Statistics. "Much of the recent increase in import prices can be attributed to the depreciation of the dollar."

He noted that the price increases accelerated in the last three months of the year as the value of the dollar fell sharply. Prices for foreign machinery and transportation equipment, the largest nonenergy component of imports, rose 2.4 percent from September through December after increasing 0.2 percent in the previous three months.

Prices for imported chemicals increased by 12 percent last year after declining for the past three years. Intermediate manufactured products -- iron and steel and other metals, textiles, and leather and furs -- jumped 13.3 percent last year compared with a 4.5 percent rise in 1986. Textile import prices jumped 3.4 percent in the last three months of the year, the largest quarterly increase since 1979.

These price increases are important for the competitiveness of domestic manufacturing industries because it gives them a chance to recapture U.S. sales that had been lost to lower-cost imports.