"This election can be regarded as a referendum" on the SALT II arms control treaty pending before the Senate, Defense Secretary Harold Brown said yesterday.

Given the prominence of SALT II among campaign issues, Brown contended at a luncheon of the Overseas Writers group, the reelection of President Carter could represent a popular "mandate" to get the treaty ratified.

Republican challenger Ronald Reagan has said he cannot accept SALT II in its present form because it gives the Soviet Union the edge in strategic weaponry, the long range bombers and missiles that carry nuclear warheads.

Brown's speech yesterday was part of a stepped-up effort by the Carter administration to portray the pending treaty as a step back from nuclear war, a step that Reagan would not take if he were elected, according to his critics.

Brown said failure to implement SALT II would have such dire conquences as these:

An additional expenditure of from $30 billion to $100 billion over the next 10 years as the United States tried to match an unbridled strategic buildup of the Soviet Union.

"Enormous pressures to scrap the 1972 Antiballistic Missile Treaty, which is a bulwark of strategic stability" as both the United States and Soviet Union tried to protect their land-based missiles from the thousands of extra warheads that would be aimed at them.

Gaps in nonnuclear forces -- the ones for fighting a conventional war -- as the Pentagon robbed Peter to pay Paul to buy new strategic weaponry.

A jump from 8,600 warheads in the Soviet arsenal to 10,000 by 1985 and from 14,000 to 17,000 by 1990.

Summing up, Brown said that without SALT II, "maintaining the balance would require more systems, entail higher costs and involve greater risks, and in the end would give us less rather than more security."