U.S. manufacturing companies increased their investments abroad -- particularly in Canada -- during 1980, according to a report by The Conference Board, a corporate research organization.

The number of foreign investment projects announced in 1981 increased to 252, compared with 159 the year before. Although no total dollar value was given for the projects, the report set the value of 54 percent of the projects at $18 billion.

The board said that American firms had significantly escalated investment in Canada. In 1980, 20 percent of the investments abroad were in Canada, up from about 9 percent in 1979.

Most of the investment was in Western Europe, which accounted for 44 percent of the total. That share had declined from 1979 when 53 percent of the investment went there.

The leading choices for investment were the United Kingdom, Ireland and Japan.

The report also noted that smaller U.S. firms are more frequently investing in overseas projects. "Some of these smaller enterprises are in high-technology fields, in medicine, instruments, laser techniques and computer parts," said James Green, executive director of The Conference Board's international business management program.

Green said foreign governments actively seek such firms because of growth potential and because they can make decisions on issues such as relocation more rapidly than larger firms.