The emigration of Jews from the Soviet Union reached its highest level in nearly two years last month, according to State Department figures.

In April, 166 Jews left, compared with 97 in March. The March-to-April jump represents a 71 percent increase over the month before, and the peak, thus far, of a slight but gradual rise since the beginning of this year.

Jewish exits from the Soviet Union last showed such a sharp increase in July 1983, when 167 left. A U.S. official said the April emigration tally was "more reminiscent of figures in 1982," after which Moscow allowed fewer to leave.

Since 1979, when 51,320 Soviets Jews were granted exit visas, Soviet emigration has taken a sharp decline. In 1984 about 900 Jews left the Soviet Union, compared with 1,314 the year before.

A State Department official called the April emigration increase "encouraging" but quickly added, "We would like it to be a lot more, and we'd like it to be sustained."

The official added that besides last month's increase, the State Department has noted two other "modest," encouraging signals from Moscow regarding emigration. More than the usual number of "refusedniks," or Soviets who previously have been denied exit, are now leaving, and there has been a jump in the number of Moscow residents among recent emigres. Of the 166 who emigrated last month, 120 came from Moscow, a State Department spokesman said.

However, while the numbers of visas issued for residents of the capital have increased, reportedly they have decreased elsewhere in the Soviet Union.

Another U.S. diplomat suggested that in allowing an increase in emigration, the Soviet Union is "signaling an improvement in human rights." The number of exit visas granted by Moscow is one of the yardsticks western diplomats use to measure the course of East-West relations.

A perceived thaw in U.S.-Soviet relations following the resumption of arms talks in Geneva and the accession to power of Mikhail Gorbachev has spawned rumors in Moscow that a much stronger surge in emigration will begin soon.

Bill Kaiserling of the National Conference on Soviet Jewry said he was "encouraged" and "grateful" that there was an increase in emigration last month. But he added, "We don't know whether it will continue." Rather than to "get too excited," he said, "we're watching the situation closely."