The Soviet Union's attempt to harness the power of the hydrogen bomb is lagging, after a quick start that gave it world leadership for most of the last 10 years.

The Soviets are no longer ahead in the race to see which country first will produce power from fusion; they are now behind the United States and almost certainly will stay in second place for at least the next 10 years.

Touring American journalists who visited the Kurchatov Institute on the western edge of Moscow recently were told that the Soviet program to tame the fury of fusion is almost at ta standstill. The Soviet Tokomak machine used in fusion research at Kurchotov has been unable to reach temperatures beyond 13 million degrees, far less than the 60 million degrees, reached last summer at the Tokomak at Princeton University and light years distant from the 100 million degrees scientists say is necessary to achieve fusion.

A program is under way to double the temperatures achieved here to 26 million degrees, but the T10 Tokomak will get no hotter than that and will not get that hot before 1983. By that time. A bigger Tokomak than the one already in place will be operating at Princeton and may have reached the magic mark of 100 million degrees for pulses that last at least one second.

"We will not exceed the Princeton temperatures, even with our new machine. "Boris Kadomtsev, director of the plasma physics division of the Kurchatov Institute, said. "We expect the first demostration of fusion power to come from Princeton.

Temperature of at least 60 million and as much as 80 million degrees were reached repeatedly at Princeton last July. One way the Princeton Tomak roughly the Russian word for "doughnut shaped machine," achieved its record temperature was to superheat the deuterium gas confined by huge magnets with neutral subatomic particles striking the gas at fanatastic speeds.

The Soviet Tokomak does not posses the neutral particle "guns" used at Princeton and developed at the Oak Ridge National Laboratory in Tennessee. In 1983, the Soviet plan to heat deuterium gas using short-wave radio beams, an elegant method that willheat the gas its anticipated 26 million degrees but no more.

The Soviets also have little experience with the superconducting magnets of the kind used routinely at Princeton to contain the superheated gas (called plasma) and keep it from touching the walls of the Tokomak machine. A small machine here at the Kurchatov Institute has experimental superconducting magnets but they are nowhere near the size of magnets needed to contain fusion temperatures.

The first use of large superconducting magnets will be in the newertiom device that will start up in 1983 at the Kurchatov institute, which is named for one of the fathers of the Sovied atomic bomb, Igor Kurchatov.

The United States has not always held such a commanding lead in the race to extract electricity from the heat of a controlled thermonuclear explosion. It was the Soviets who conceived of the doughnut shape for a machine to confine the enormous heats produced when hydrogen atoms fuse, and Princeton's Tokomok was derived from this idea.

Money is one reason, the United States managed to pass the Soviets in fusion. The U.S. program has been enlarged over the last five years, while the Soviet program has appeared to shrink. Western observers think the Kremlin money managers drained cash from the Soviet fusion effort to support other energy research that promises a quicker payoff. Fusion experts predict commercial fusion power no sooner than the second decade of the 21st century.

Kadomtsev made it clear in his talk to American journalists that the Soviet fusion program is shifting away from the pure fusion electricity approach to what he called a 'hybrid' plan to use fusion neutron energy to bombard blankets of uranium or plutonium wrapped around a fusion device.

The enormous number of neutrons released in a fusion reaction would overwhelm the uranium and plutonium blankets in such a way that the blankets would breed more plutonium, as much as 10 times as much plutonium as was used in the original blankets. The plutonium could then be used in nuclear powr plants to make electricity.

This is the same concept that is behind the fast breeder reactor except that it is 10 times as efficient. The best a breeder can hope to get is twice as much plutonium from the fuel it burns in roughly a 10-year period.

BUt even here, the Soviet progress is not firm. Originally, the Soviets talked of building their own bybrid machine (known on paper as the T20) but how they speak of raising the billions of dollars it will take to build the first hybrid from an international partnership that includes the United States, Japan, and most of the nations of western Europe.

"We would like to construct such a machine right here at Kurchatov where all the countries would bring their own blankets to produce plutonium," Kadomtsev said. "We think that if the international community gets behind such a concept we can be producing plutonium as much as seven years before the first commercial fusion electric plant is built."