With consumption tapering off at home, U.S. tobacco companies have looked abroad and dramatically increased their share of the world cigarette market in recent years, a federal study said this week.

Examining a four-year span from 1986 to 1990, the U.S. International Trade

Commission found that "during this period, the United States became the leading cigarette exporting country in the world."U.S. cigarette sales abroad mounted steadily throughout the period, culminating in a 41 percent surge in 1990, with sales valued at nearly $4.8 billion, double what they were in 1980.

Meanwhile, domestic consumption dropped to the lowest level since 1942 as a vigorous anti-smoking campaign by both private health groups and the federal government, combined with higher prices, persuaded more Americans to kick the habit.

Successful marketing and a helping hand from the office of the U.S. Trade Representative account for much of the industry's boom abroad.

Trade representative probes of tobacco exports to Japan, South Korea, Taiwan and most recently Thailand, where negotiations are not yet complete, have led to liberalization of those markets.

Japan and other Asian countries were destinations for about 40 percent of U.S. cigarette exports in 1990, the trade commission said.

Marketing campaigns have wooed customers in many developing nations, the

commission noted. As income rises in these countries, so does the interest in high-quality American cigarettes.

Tom Slane, vice president of the Tobacco Merchants Association, said he expects the trend to continue as the milder-blend American cigarette "is sort of taking over."

Mr. Slane refused to comment on whether the industry had redoubled its hunt for markets abroad due to dwindling interest at home, saying the U.S. has always been a strong exporter of tobacco.

The trade commission also found that tobacco manufacturers trimmed their work forces during the period, employing just 30,000 people in 1989 - the latest year for which figures are available.

The United States produces 12.5 percent of the world's cigarettes, ranking second only to China, which churns out 30 percent of cigarettes.