Chancellor Helmut Schmidt, in a last-ditch attack on opponents preparing to oust him this week, charged today that a new Christian Democratic-led government would mean a significant break with previous policy, bringing far-reaching changes in international politics and social and economic developments in West Germany.

Speaking at a closed-door meeting of his Social Democratic Party's national council, Schmidt dwelt on the economic costs he said would accompany conservative rule--including higher value-added taxes and more state borrowing--and argued that any signs of economic upturn would be illusory.

The party council, in its own statement, added that a government led by Helmut Kohl, chairman of the Christian Democratic Party who is expected to succeed Schmidt, could not be expected to continue Bonn's foreign policy, which the statement described as arguing West German interests forcefully in the Western alliance while undertaking initiatives with East Bloc states.

The statements appeared intended to dramatize the effects of the shift to a new center-right coalition being anticipated here following the withdrawal Friday from the government of all four Free Democratic Party ministers. The Social Democrats had ruled in a coalition with the Free Democrats since 1969.

By stressing the gravity of the change, Social Democratic leaders presumably hope to gain public support for new elections that Schmidt has suggested be held before a new government is formed. They also would seem to be signaling the outlines of their campaign offensive against the Christian Democrats.

A hint emerged that the controversial planned stationing of new nuclear missiles in West Germany might be turned into an election issue by the Social Democrats. The party council's statement said: "Every German chancellor has the duty to do whatever is humanly possible to see that no additional rockets need be stationed on German soil."

Claiming a groundswell of popular support for Schmidt's call for immediate elections, the Social Democrats released a weekend survey by the respected polling organization, the Infas institute, showing that 78 percent of West Germans favored the idea. Only 19 percent were reported to back the idea, put forward by Kohl and Free Democratic Party leader Hans-Dietrich Genscher, that a new government should be formed first to manage urgent economic problems.