In a statement keyed to U.S.-Soviet talks that open in Geneva on Monday, Soviet President Konstantin Chernenko warned today that the start of an arms race in space would create "an irreversible situation . . . fraught with the most baneful consequences."

Chernenko's comments, which came as Soviet officials led by Foreign Minister Andrei A. Gromyko were completing preparations for the two days of talks, were contained in a message to a group of clergymen distributed in English by the official news agency Tass.

The Soviet leader noted that "the Soviet Union attaches much importance to reaching agreement with the United States on the entire range of questions embracing both the nonmilitarization of space and nuclear arms."

Reiterating Soviet concern about U.S. efforts to develop a space-based defense against missile attack, Chernenko declared: "There has arisen the need to adopt urgent and effective measures to prevent a further destabilization of the strategic situation and preclude further rounds of the arms race."

He stressed that the Soviet approach to talks "is based on the conviction that they should be honest and businesslike. The aim of the talks should not be to deceive [one's] partner and public opinon."

[An unusually large U.S. delegation, led by Secretary of State George P. Shultz, arrived in Geneva Sunday.]

Earlier today, the Soviet press voiced other concerns about the forthcoming talks and sought to boost Moscow's case that space weapons will be the centerpiece of the discussions.

A commentator in the Communist Party daily Pravda suggested that the United States may drag its feet in reaching an accord with the Soviets, adding that the U.S. position is "not clear at the moment."

"It is also worth recalling that these days American officials ever more often make it clear . . . that Washington is in no hurry to work out mutually acceptable proposals," wrote Yuri Zhukov.

Zhukov noted that halting the arms race in space "inevitably" will be the central issue in the Geneva talks, echoing the consistent Soviet position that has put President Reagan's Strategic Defense Initiative -- popularly called "Star Wars" -- at the top of the Soviets' agenda.

In the days before the Geneva meeting, the Soviet press steadily has prepared a case for holding the United States responsible if the Geneva meeting does not produce prompt agreement for future talks.

"The Soviet Union is ready to conduct talks in a constructive way. It will not be found wanting. As for the United States, its stand will become clear only in the course of the coming meeting," Zhukov wrote.

Tass also took note of the opposition in Western Europe and in the United States to the Star Wars program, while at the same time underlining the Reagan administration's attachment to it.

"How interested the U.S. administration is in easing international tension and how prepared it is for a really constructive dialogue with the Soviet Union . . . will be shown in the next few days," Tass said.

Some diplomats said the Soviets' tactful handling of the embarrassing flight of one of its cruise missiles over Scandinavia last week was an indication of how much importance they attach to the Geneva talks.