The United States' merchandise trade deficit climbed past $100 billion for the first time ever last month and appeared headed for a new yearly high of $130 billion, the Commerce Department reported yesterday. But Commerce Secretary Malcolm Baldrige predicted "the worsening trend should slow next year."

Other analysts, however, took a less rosy view of America's trade future. "I don't think it's the other side of the mountain," said Commerce Department economist David Lund, a specialist in international trade.

David Ernst, a vice president with Evans Econometrics, predicted next year's trade deficit will grow to $150 billion as the high value of the dollar continues to pull in imports and hurt U.S. exports by making them more expensive overseas.

The 10-month deficit of $105.5 billion is almost twice as high as the $55.5 billion splash of red ink in the same period last year. At that rate, the annual level will soar even higher than predicted, to $140 billion, Baldrige pointed out.

The new high for the first 10 months of 1984 came despite October's pronounced dip in imports and the second-best export performance of the year. The trade deficit for the month fell to $9.2 billion, a $3.5 billion drop from September and 25 percent below the monthly average of $12.2 billion for the third quarter of 1984.

Ernst, who called the dip in the monthly trade deficit for October "good news and surprising," said it was probably caused by the slowdown in economic activity, which decreased the demand for imports.

October's imports totaled $27.6 billion, the lowest level since June and a drop of $3.3 billion from September. A seasonal increase in overseas petroleum purchases -- up 11.4 percent -- kept the import totals up against downward pressures from declines in shipments of manufactured goods such as cars, clothes, telecommunications equipment and electrical machinery.

Exports for October reached $18.4 billion, a $200 million increase over September. Overseas sales of power generators, electrical machinery, office machine parts, data-processing equipment, telecommunications equipment, and farm products such as corn, cotton, soybeans and tobacco, registered increases in September.

Nonetheless, Baldrige said "foreign sales remained sluggish as the strong dollar cut potential gains from cost-reduction efforts at home and somewhat faster economic growth abroad."

The overheated dollar is hurting American sales abroad even in areas such as capital goods where it once dominated world markets, he continued. "The slight surplus of $87 million in the third quarter contrasts sharply with the $25.1 billion surplus for all of 1983 and the record $44.6 billion surplus in capital goods trade in 1981," he said.

"These continuing problems underscore the need to cut the budget deficit to reduce interest rates further to lower the dollar."

U.S. Trade Representative William E. Brock cited the $200 billion budget deficit as a major cause the trade deficit. "I think the trade deficit could be eliminated if we could eliminate the fiscal deficit," he told reporters earlier this week.