Sen. John Glenn (D-Ohio) reversed himself yesterday and publicly endorsed the SALT II treaty while calling for the United States to press for sharp reductions in nuclear arms, a position that brings him close to supporters of a nuclear freeze.

Glenn, who plans to formally announce his candidacy for president Thursday, voted against SALT II in 1979 in the Senate Foreign Relations Committee, saying he feared the Soviets could easily cheat on the treaty.

The treaty between the United States and the Soviet Union was approved by the committee but never reached a vote on the Senate floor. It remains unratified.

"The president," Glenn said in the Democrats' weekly Saturday radio broadcast, "has said that we will continue to abide by those limits in SALT II as long as the Soviets do the same. But this kind of informal commitment is not enough. That is why I am today calling on the president to formalize our commitment to the SALT II limits, either through executive order or by supporting ratification of the treaty by the U.S. Senate."

Glenn added that he believes additional limits can be placed on nuclear arms, saying, "We cannot allow a freeze to mark the end of our efforts."