The Carter administration began a major campaign yesterday for expansion of NATO's medium-range nuclear missile force in Europe, while warning that Senate defeat of the SALT II treaty or delay in its approval would work against any plan to modernize NATO's nuclear force.

Taking part in the drive were Defense Secretary Harold Brown, in testimony before the Senate Foreign Relations Committee; Vice President Mondale and national security adviser Zbigniew Brzezinski, in speeches to the Atlantic Treaty Association; and President Carter, in remarks made at at his Tuesday new conference endorsing the NATO scheme.

In the strongest administration statement addressed to the European defense issue to date, Brown told the Senate committee that, unless the SALT treaty with the Soviet Union is approved promptly, it will be impossible to get the necessary Western European support for the deployment on the continent of new ballistic and cruise missiles to match recent Soviet advances in comparable weaponry.

The administration campaign and the day's remarks brought together several intersecting themes and goals: the advancement both of SALT II to limit strategic weapons and of the drive to increase sub-strategic medium-range weapons in Europe; a response of Soviet President Leonid I. Brezhnev and rebuttal to the attendant Soviet media campaign, and a harder anti-Soviet position at home of potential benefit to an embattled president under heavy criticism for his handling of the troops-in-Cuba issue.

Brezhnev, for his part, cautioned against the likelihood of Soviet political intimidation of the nation's European allies as a result of Soviet millitary superiority.

In language decidedly more provocative than that used by the president during his new conference the day before or the vice president just hours earlier, Brzezinski said NATO must choose between "passivity" or "effective action now" to deploy American medium-range missiles "capable of reaching Soviet territory."

Brzezinsky's speech to the Atlantic Treaty Association, like Mondale's remarks to the same group and Carter's statements Tuesday, amounted to U.S. response to Brezhnev's proposals of last Saturday.

Brezhnev announced a unilateral reduction in Soviet troop and tank levels in East Germany, and appealed for a halt to the proposed increase in NATO missile systems. He promised reductions in Soviet missile deployments in return.

Brzezinsky charged that the Soviets have under way "a substantial and sustained program to modernize, expand and deploy" their medium-range nuclear forces targeted against Europe. He called the new SS20 missile being deployed by Moscow "an enormous advance" over previous weapons, and said the sustained Soviet effort "goes well beyond what could be explained as meeting a reasonable defensive need."

NATO, in the face of this, has done virtually nothing to upgrade its own European theater nuclear forces, he said.

Beyond the military challenge, he said, the chance for Soviet political pressure would increase "should NATO be viewed as unwilling or unable to respond to threats of nuclear warfare confined to the European area, as the lack of any effective theater forces would certainly make it appear to be."

Mondale, in his address, said "the self-restraint in theater nuclear forces shown by the NATO alliance over the past two decades has not been met by corresponding restraint on the part of the Soviets." The vice president called the decisions on missile modernization and arms control to be made by NATO later this year "crucially important."

While saying the the United States would welcome the unilateral reductions announced in East Berlin by Brezhnev last Saturday, Mondale said it is aboslutely essential that the step be seen in the context of of a large and growing Soviet armed presence in Europe.

"It is obviously in the Soviet interest to lure NATO away from crucial conventional and theater force modernization," Mondale said.

Brown told the Senate committee that the NATO allies would look upon ratification of SALT as proof that the United States can conduct a coherent national security policy, and as a sign that the prospect for eventual negotiated reductions in "theater nuclear forces" in Europe is favorable.

Brown said yesterday, as some European defense analysts already have, that there would be no incentive for NATO to agree to new deployments of improved missiles in Europe if the United States and Soviet Union abandon the SALT process in favor of a new round of strategic arms competition.