Forget the spaghetti western. A real international pasta war is boiling over.

The National Pasta Association has filed a formal complaint with the federal government alleging that the European Common Market is illegally subsidizing Italian pasta, enabling the Italians to compete unfairly in the U.S. market.

Faced with what they see as a growing threat to their share of a billion-dollar-a-year industry, the American manufacturers are not just noodling around like a bunch of meatballs. They have engaged a Washington lawyer, Paul D. Cullen, to press their claim of illegal subsidies through the office of the U.S. Trade Representative.

In a petition filed last Friday, Cullen charged that the Common Market is violating international law not just in subsidizing Italian pasta exports but also in its subsidies of other processsed food products exported to the United States.

The trade representative's office has 45 days to review the petition and decide whether the government will pursue the complaint through international trade channels. Officials there said the Common Market does subsidize agricultural exports, but the General Agreement on Tariffs and Trade prohibits subsidies of processed or "nonprimary" food products. The question is whether pasta fits that category.

If after fact-finding and conciliation proceedings the U.S. concludes that the export subsidies are illegal and the Europeans continue them, the president could impose trade sanctions on Italy. The Common Market has not yet responded to the complaint.

State Department officials familiar with European trade policies said the pasta-makers' complaint is only one small strand of a complex problem afflicting trade relations between the United States and Europe. U.S. steel manufacturers, for example, have complained of unfair competition from subsidized and state-owned European steel makers, and Europeans have complained of allegedly unfair competition by U.S. products subsidized through such techniques as controls on the price of natural gas.

Department of Agriculture figures show that imported spaghetti and noodle products account for only about 3 percent of U.S. sales. Many Washington-area supermarkets and grocery stores do not even carry them. But Cullen said subsidies have contributed to a "dramatic increase" in pasta imports.

Lester Thurston, chairman of C. F. Muller Co., a major pasta maker, and president of the National Pasta Association, said that in 1979 and 1980, Italian imports rose 34 percent while sales of U.S.-made products stayed even.

"In the specialty shops, especially on the East Coast, and in the ethnic neighborhoods, there has historically been an imported presence," he said, "but it was stable. It did not grow year to year. But in the past few years we have become aware of a substantial increase in the visibility of imported products."

Ironically, much imported pasta is made from U.S. wheat. Italy, faced with a poor wheat crop this year, increased its purchases of U.S. durum from 5 million bushels to 16 1/2 million.