U.S. companies are seeing their share of the global telecommunications market decline, an erosion that could ultimately prove dangerous to the health of the American economy, according to a Commerce Department report issued yesterday.

Pointing to a $1.9 billion U.S. trade deficit in telecommunications, the study attributed the decline to foreign trade barriers, lagging U.S. research investment and slow productivity gains.

"This report represents a very strong statement on the part of the Department of Commerce that telecommunications is one of our cutting-edge industries and has also historically been a stellar performer," said Janice Obuchowski, assistant secretary and director of the office that co-authored the report. "But we need to tend to some macroeconomic factors."

Obuchowski called the report, ordered by Congress in 1988, the Commerce Department's clearest signal yet that it believes the administration should approve changes in the domestic telecommunications regulatory environment.

The report included a package of general recommendations for government and industry, particularly in lobbying for the opening up of foreign markets. It also linked the failure of the United States to match manufacturing productivity gains in Japan and Britain to a "troubling" decline in American educational standards.

Among its recommendations, the study advised telecommunications companies, which account for 5 percent of the U.S. gross national product, to focus toward long-term investment and research instead of short-term returns.

The timing of the competitiveness report was considered particularly important since it comes amid congressional and judicial debate over the modification of limits on competition among the so-called "Baby Bell" regional phone firms.

Spokesmen for two of companies, Bell Atlantic Corp. and Ameritech Corp., welcomed the study and said it is further evidence that more competition is needed in the manufacturing of telecommunications equipment, an area that the regional companies have sought to enter.

"It fits in very well with what we've been saying," said Patricia C. Rimo, spokeswoman for Bell Atlantic. "One of the points that the report makes is American manufacturing in telecommunications often doesn't integrate {research and development} product design and production processes," she said.

Legislation now before the Senate sponsored by Sen. Ernest F. Hollings (D-S.C.) proposes relaxing limits on the regional telephone companies, allowing them into the manufacturing business.

U.S. Federal District Court Judge Harold Greene also is considering whether to alter restrictions on information services that limit the ability of the regional phone companies to enter the business.