The Soviet Union feels nature played a dirty trick when it sent the waters of its mighty rivers flowing north into the Arctic Ocean instead of south toward a vast region of sun-parched lands.

"It is a historic, natural injustice, which we should correct," Palad Palad-Zade, deputy minister of land reclamation and water conservation, said in a recent interview.

The injustice now has taken on even greater urgency as the Soviet Union, hurt by a series of bad grain harvests, expands its program to irrigate the steppes of Central Asia.

"We have 84 percent of our water resources located on the northern slope, where it is not much needed, but the main economic potential -- industry, population, agriculture, and naturally, the opportunity to develop irrigation -- is in the south, where only 16 percent of the water resources are located," said Palad-Zade.

With a dwindling supply of local water resources, Central Asia's promising potential may be threatened -- unless a way is found to send the northern waters south.

But how? Soviet -- and before them, czarist -- planners have puzzled over the issue for decades. And by all indications, the debate is still going on.

The scheme to divert Soviet rivers (Palad-Zade bridles at the term river reversal) has two components. In European Russia, plans already are approved for the first stage of a project that will carry water from the Sukhona River and the Onega and Ladoga lakes into the Volga, and on down to the Caspian Sea.

The European project, estimated to cost $780 million, will carry water through a series of canals, including one between the Volga and the Don, to irrigate more than 2.5 million acres in the northern Caucasus, Palad-Zade said. The completion date is set for 1990.

The fate of ancient monuments in the area has been a matter of concern, but Palad-Zade insisted that they will be protected.

The second project, more ambitious and controversial, would involve the Ob and Irtysh rivers in western Siberia. There, where the miles-wide waterways sluice through vast underpopulated regions, the Soviets have been dreaming for years of a construction project that, if undertaken, would be one of the largest the world has known.

The current proposal is to build a canal 1,584 miles long, 49 feet deep and 656 feet wide, running from the Ob and Irtysh to the arid regions around the Aral Sea.

The technological and engineering feats involved in its construction are staggering. Crossing the foothills of the Urals, the canal would rise 328 feet and, as it reaches the Central Asian steppes, branch off into a complex array of subsidiary waterways. The cost is estimated at $40 billion.

Both the European and the western Siberian projects were mentioned in passing at the recent plenum of the Soviet Communist Party Central Committee, devoted to land reclamation. The plenum's report confirmed that the first stage of the Volga project now is proceeding. The future of the Siberian project, however, is less clear.

In the interview, Palad-Zade, whose ministry historically has pushed for large irrigation projects, emphasized that final approval of the Siberian plan still lies ahead.

"Such a project is now being worked on . . . it is now under design. When we finish the plans, then it will be clear when we will build, if we will build or not build," he said.

Controversy has surrounded the Siberian river project since its inception. First advanced in the 1950s as a transportation route and source of hydroelectric power, the canal plan was revived in the 1970s for water distribution.

Critics, writing in the Soviet press, raised a number of objections. From western Siberia came complaints that the plans would "sharply diminish western Siberia's resources and make the environment a good deal worse." Fishermen have been opposed, predicting a drop in their catch. Other critics cautioned about the need to pay close attention to ecological consequences, to learn from the Soviet Union's past mistakes in water management.

The most dramatic concern of all, raised both here and in the West, is about the possible impact of the Siberian plan on the northern climate. By taking water from the Ob, the canal would reduce the amount of fresh water flowing into the Kara Sea, decreasing the amount of ice formed there. Hypothetically, this could affect weather patterns in the Arctic region.

Palad-Zade discounted these views as alarmist.

"This absolutely does not pose any danger to the climate. The global climate is formed by completely different laws and completely different factors," he said.

Palad-Zade noted that the plan, as now envisioned, would draw only 6 percent from the rivers' flows, less than the year-to-year fluctuation of 10 to 15 percent.

"Therefore, nothing damaging will happen to the rivers or the region where this water will be taken, but quite the reverse: it will be an improvement," he said, noting that the project would serve to drain Siberia's unusable marshlands.previously.

Palad-Zade said these conclusions were reached "unanimously" by 150 scientific research institutes collaborating on the project.

Western analysts here take this to mean that the Soviets have given the project an ecological seal of approval. "Now, if they don't go ahead with it, it will be because of the expense, not because of the environment," said one western analyst.

Without access to all the facts, non-Soviet scientists hesitate to confirm or dispute the Soviet conclusions. But, according to a published report, one American scientist who spent five months here analyzing the Soviet research has tentatively agreed with the finding on the climate question.

There is a strong lobby for the Siberian project. The Central Asian republics, with their fast-growing populations, need the water for cotton and other crops. And there has been recent evidence that local water resources in these southern regions are fast running out. For instance, a 1978 article noted that turbines at a hydroelectric station on the Naryn River had to be shut off because the reservoir was too low.

The European and Siberian projects also would help solve another problem: the shrinking of both the Caspian and Aral seas.

Palad-Zade cited the problems of the Caspian Sea as one of key reasons for going ahead with the replenishing of the Volga. And scientists have expressed concern that unless it too is replenished, the Aral Sea will turn into a flat salt marsh.

Irrigation, in the Soviet Union as elsewhere, can be a mixed blessing. As water runs across desert land, it brings minerals and salts to the surface that can be damaging. This is particularly true of the open irrigation systems prevalent in the Soviet Union.

Salinization already is a major problem in Central Asia and, according to some western analysts, the benefits of increased irrigation may be short-lived.