Four senators yesterday wrote President Reagan that abandoning SALT II ceilings for multiple-warhead missiles would ". . . cast a pall over the arms talks in Geneva, seriously damage important U.S. foreign policy interests" and end superpower restraint on deployment.

Republicans John H. Chafee (R.I.) and John Heinz (Pa.) and Democrats Dale Bumpers (Ark.) and Patrick J. Leahy (Vt.) were responding to statements by Reagan and Assistant Defense Secretary Richard N. Perle questioning whether the United States should continue observing limits in the 1979 arms-control agreement.

Reagan's decision on continuing SALT II adherence when it expires Dec. 31 is affected by scheduled sea trials of the Trident missile submarine Alaska in late September. The Alaska is to carry 24 missiles with multiple warheads, placing the United States above the 1,200 limit in SALT II for such missiles. Reagan must retire an older missile submarine or Minuteman missiles to respect the ceiling.

While noting U.S. "legitimate concerns" about Soviet compliance with arms-control treaties, the senators said, "There is no question that the Soviets have remained within the multiple independently targetable reentry vehicle ceilings of SALT II and other important limits. This is especially important because the Soviets are just below the 820 limit on MIRVed intercontinental ballistic missiles, having 818."

In view of the Soviets' "impending deployment of the MIRVed SS24, our violating the 1,200 limit would openly invite them to violate the 820 limit, which they are well-positioned to do," the letter said.