Sen. Daniel Patrick Moynihan (D-N.Y.) took the unusual step yesterday of defending himself on the Senate floor against a fellow senator's charge in a television interview that Moynihan was one of the Senate's "weakest" supporters of defense spending.

Sen. Phil Gramm (R-Tex.), who made the charge in an appearance with Moynihan on NBC News' "Meet the Press" program Sunday, was not present to hear Moynihan.

A spokesman for Gramm said he did not know about Moynihan's remarks in advance but would stand by what he said Sunday.

Moynihan said a "half-dozen" Republican senators had "expressed their regret" that the exchange took place. None did so on the Senate floor, however, although several Democrats, including Minority Leader Robert C. Byrd (D-W.Va.), rose to praise Moynihan's record and warn against personal attacks by one senator against another.

If debate becomes personal and undermines the Senate's customary courtesies, "this Senate will continue going downhill," Byrd said.

In a measured response that contrasted with his angry retort to Gramm during the Sunday interview, Moynihan cited his military service record, including volunteering for active duty at age 17 during World War II, and his support for military appropriations bills. Of the nine defense spending bills that have passed since he came to Congress, he said, he opposed only the one for fiscal 1984 because it included funds for deployment of the MX missile in Minuteman silos.

But he also invoked the specter of the late senator Joseph R. McCarthy (R-Wis.) in warning, without direct reference to Gramm, against "name-calling, accusation and innuendo" in the conduct of legislative business. "We lived through that in the period of Joe McCarthy," he said.

"We are Americans on both sides of the aisle. We will not have our patriotism impugned, our records misrepresented."