Moscow's chief delegate to the coming talks on reducing nuclear arms said here today the Soviet Union is in favor of a Soviet-American agreement that would provide for substantial reductions in strategic arms and at the same time set effective limits on the "qualitatative improvement" of such weapons.

The remarks by Ambassador Viktor P. Karpov, although echoing some well-known Soviet positions, accentuated the positive prospects for an agreement. His commments did not contain the sharp criticism of American proposals that have appeared in earlier Soviet speeches and commentaries.

Karpov made a statement and answered questions from reporters at the airport here on arriving for the talks that open Tuesday.

Those talks will deal with reducing the nuclear intercontinental-range missiles of both superpowers. President Reagan has labeled them the Strategic Arms Reduction Talks, or START, because he wants big cutbacks in the number of missiles and warheads on both sides. But Reagan's proposal for equally sized forces would require much bigger cuts by the Soviets in their most threatening land-based missiles, where they now have an edge.

While endorsing the idea of reductions, however, Karpov called the talks by a different name and thereby emphasized the strong Soviet view that, as a step toward reductions, the United States should ratify the treaty from the second strategic arms limitation talks, or SALT II. That treaty, signed by then-president Jimmy Carter and President Leonid Brezhnev in 1979, was never ratified by the United States. It would have put a limit on the number of missiles in each arsenal at roughly today's levels.

Karpov said his delegation was here "to hold strategic arms limitation and reduction talks . . . and thus to continue the process initiated by the SALT I and SALT II agreements so vital to peace."

The Reagan administration does not want the SALT treaty ratified because, in Washington's view, it would legitimize the Soviet lead in big land-based missiles that is allowed under the SALT ceilings. Moscow's goal appears to be to retain the SALT levels and to stop deployment of new American weapons meant to restore the edge in atomic power that Reagan believes the United States has lost.

By mentioning SALT here several times today, Karpov also seemed to be appealing to the sizable number of American members of Congress who would still like to see the SALT treaty ratified or a nuclear freeze put in place.

The American negotiating team here, which is headed by retired Army Lt. Gen. Edward Rowny, is known to be concerned about recent votes in House committees supporting such a freeze. Rowny believes such votes will weaken his hand as a negotiator because Moscow will try to encourage the freeze movement and wait to see how it comes out.

Karpov also made use of Moscow's earlier pledge not to be the first to use nuclear weapons, stating that "if other nuclear powers follow this example, the possibility of the outbreak of nuclear war will be brought to nought." The U.S. government and its allies have rejected the Soviet pledge as a tactic because Moscow has superiority in conventional forces in Central Europe and thus can renounce the use of nuclear weapons more easily than the West.

Karpov said, "It is exceptionally important to set the right tone . . . from the very outset" of these talks to improve the chances for success. "It doesn't suffice to just claim to be ready to negotiate," he added. "What is most important is to endeavor in practice to reach tangible and mutually acceptable agreements."