Clearly aiming at maverick Romanian leader Nicolae Ceausescu, Soviet President Leonid Brezhnev tonight sharply rebuked those who make "demagogic arguments" against increased defense spending by the Warsaw Pact.

Brezhnev, in a speech at a state dinner in the Kremlin for visiting Afghan leaders, declared that Moscow will not "agree to the weakening of our defenses in the face of the growing military might of imperialism, no matter by what demagogic arguments such calls are camouflaged."

Ceausescu is in a widening confrontation with the Kremlin over his wellpublicized opposition to proposed increases in the Warsaw Pact's defense budget and increased integration of East Bloc armies.

Brezhnev's remarks raise that disagreement to the highest level here and are his first direct comments on the breach, which occurred at the Kremlin in late November during a summit meeting of the leaders of the seven alliance countries. The Soviet leader's words are an implicit warning to other pact nations, as well as the Romanians, of the seriousness with which the Russians view the disagreement.

Fueling the Soviet reaction is unabated Kremlin anger at Ceausescu's diplomatic moves toward the Kremlin's archenemy, China. Peking leader Hua Kuo-feng visited Bucharest in August in a major demonstration of Ceausescu's maneuvering to forge a foreign policy independent of the Kremlin and its interests. His opposition to increased defense spending is connected to that effort. as well as to his own internal economic problems. Romania has been hit by strikes and protests in recent years among a populace that may have the lowest standard of living of any East European country.

The authoritative International Institute for Strategic Studies placed Romanian defense spending this year at $923 million. Ceausescu has said in speeches made in Romania since his return from the Moscow summit that the international situation does not call for increased spending.

Brezhnev declared that the Soviets "are for spending all the rubles, and dollars, zlotys and marks, lies and francs, on peaceful needs only." But he said to do so would mean unilateral disarmament at a time when "imperialism" -- the West -- is increasing its defense spending. NATO members recently agreed to a substanitial increase in military outlays to counter what Western strategists say is continued strengthening of East Bloc forces.

Brezhnev said the solution to disarmament must be mutual.

"It is precisely this stand of the Soviet Union and other fraternal countries that has found reflection in the recent decision of the Moscow meeting" of Warsaw powers, he said. His explanation is also aimed at countering the possible effect elsewhere in East Europe and in other countries of Ceausescu's carefully publicized opposition.

In keeping with the Soviet handling of its present disagreement with Ceausescu, Brezhnev, like the official press in recent days, avoided mentioning the Romanian's name.