The Soviet Union "will have to make some moves" to change its positions before progress is possible at the fifth round of the Geneva arms talks beginning today, a senior administration official said yesterday.

"We have good propositions on the table," the official said, "and it is up to them to come forward. There is no point in us negotiating against ourselves" by devising new proposals.

At the same time, however, a Soviet diplomat here said he sees little chance of progress in the talks "as long as the Reagan administration holds to its present positions."

Officials of both nations expressed uncertainty about how the recent explosion and release of radiation at the Chernobyl nuclear reactor might affect the talks.

One U.S. official said yesterday that Soviet delay in releasing information about the incident "shows up the problem in arms control and the need to agree on good verification procedures."

President Reagan, in a statement released yesterday, picked up the same theme saying, "In light of the unfortunate events of the past week . . . the need for effective verification measures has become clearer than ever."

There was, however, another view that the accident called attention to the need to control nuclear arms. "It raises the public consciousness," one official said, "and that is all to the good."

Another U.S. senior official said the Soviets "might be less forthcoming" in the talks, adding that Moscow has tended to "pull in" when being criticized.

As in the past, U.S. officials said yesterday that the best chance for progress in the new round involves negotiations on intermediate-range nuclear weapons, Soviet SS20 missiles and U.S. Pershing II and ground-launched cruise missiles based in Europe.

Reagan called on the Soviets "to get down to business by addressing seriously with us in Geneva the practical implementation of the mutual commitments which Soviet leader Mikhail Gorbachev and I made at the summit."

At that time, the two leaders agreed to work toward a 50 percent reduction in nuclear stockpiles and an interim agreement on intermediate-range nuclear weapons.

In another statement released yesterday, Kenneth L. Adelman, director of the Arms Control and Disarmament Agency, said that, after Gorbachev offered arms-control proposals in a speech Jan. 15, Soviet negotiators in Geneva "offered little explanation . . . beyond the points covered in Gorbachev's public presentation."

Adelman said, "It is difficult to avoid the conclusion that the Soviets are, at least for now, content to view arms control primarily as a means of influencing the political climate in the West."