The government's index of leading economic indicators, which is supposed to foreshadow changes in the economy, rose by 0.9 percent in October, the Commerce Department reported yesterday. This was the smallest rise in the index since it began its postrecessiion climb in June.

Some private economists said yesterday that the slackening of the index reflected a weaker economy. Soaring interest rates in the last few weeks threaten to choke off the economic recovery, according to many economists.

Meanwhile the Federal Reserve Board yesterday reported a drop in the nation's money supply in the week ending Nov. 19. This sign of a slowdown in money growth could cause interest rates to soften. Rapid money growth since the summer has led the Federal Reserve to tighten credit, thus pushing up interest rates. If the latest money figures signal a turn in the trend, then rates could soon peak.

Both narrow measures of the money supply dropped by close to $2 billion after seasonal adjustment, the Fed reported. However the money supply has still been growing faster than the Fed's target during the past three months. The narrower measure, M1-A, grew at an annual rate of 10.7 percent in the four weeks to Nov. 19 compared with three months earlier. The comparable figure for M1-B was 13.2 percent.

The money supply averaged $388.5 billion for M1-A, and $413.5 billion for M1-B in the week to end November, the Fed reported.

Courtenay Slater, chief economist at the Commerce Department, disagreed with the private economists' interpretation of the October lending indicators. w"The recovery may be slowing down," she said, but the leading indicators still rose by "a fairly healthy amount in October."

The 0.9 percent gain in October followed a revised rise of 3.1 percent in September. Originally the September rise was put at 2.4 percent. It was revised upward because of higher business formation.

Seven out of the 10 indicators in the leading index contributed to its October rise. Of the three which were weaker during the month, the series for building permits contributed most to the slower rise in the overall index. Building permits plunged by 15 percent in October. The housing industry is one of the most sensitive to interest rate changes, and the recent rise in interest rates is widely expected to slow down new construction. A separate report from the Commerce Department yesterday said that construction spending rose by 0.4 percent in October to a seasonally adjusted $225 billion annual rate. In real inflation in adjusted terms, the rise was only 0.2 percent. It came after a 4.2 percent jump in construction spending in September. The latest month's level was 6.2 percent below that of a year earlier before allowing for inflation and 14 percent down after taking account of price rises.