Kenneth L. Adelman's controversial nomination to be director of the Arms Control and Disarmament Agency moved to within one vote of approval by the Senate Foreign Relations Committee yesterday as a previously undecided Sen. Nancy Landon Kassebaum (R-Kan.) said she is "leaning toward" voting for the nominee.

Kassebaum's decision left two Republicans and one Democrat uncommitted among the committee's 17 members. Six Democrats have tentatively decided to vote against Adelman, and seven Republicans and one Democrat now appear in favor. Thus the deputy U.S. representative to the United Nations appears to need only one more vote from among the uncommitted: Sens. Charles McC. Mathias Jr. (R-Md.), Larry Pressler (R-S.D.) and Joseph R. Biden Jr. (D-Del.)

"We are now down to seeing what will do the least damage," one committee member said yesterday, "defeating him or putting him in to run the agency."

The committee is scheduled to vote Feb. 15 on the nomination. Adelman, 36, had been expected to have an easy time, but his performance during his initial confirmation hearing Jan. 27 raised questions as to his understanding of and commitment to arms control and his political stature within the administration.

As with many confirmation fights in the past, the Adelman nomination battle is being carried on in different arenas.

Pressler, for example, said yesterday the White House has become "friendly" and is "trying to accommodate my concerns" on the need for seeking negotiations on a new anti-satellite treaty with the Soviets.

That, the South Dakotan said, was far different from the time last month when he criticized the administration's decisions to fire Eugene V. Rostow as ACDA director and name Adelman. Then, he said, national security affairs adviser William P. Clark called him, said the Soviets were quoting his remarks and added that Adelman would be confirmed "almost unanimously with no problems."

Mathias, meanwhile, said he was still making up his mind. He raised questions during the hearing last Thursday as to what Adelman planned to do with the ACDA staff, where fear of a general housecleaning has existed since the Reagan administration came to town.

Over the weekend, another aspect of the battle emerged when two conservative newspaper columnists, George Will and William Safire, raised questions about the leader of the anti-Adelman committee Democrats, Sen. Alan Cranston (D-Calif.), a presidential candidate.

They cited charges Cranston made at the Jan. 27 confirmation hearing based on a report Adelman wrote in 1979 under a Defense Department contract entitled "Impact Upon U.S. Security of a South African Nuclear Weapons Capability."

Reading one paragraph in the three-page executive summary of the 76-page Adelman study, the Senate Democratic whip told the nominee: "You seem to suggest that it would be helpful to the United States, at least this is inferred from what you have written, if South Africa were to use nuclear weapons against their own blacks or against neighboring blacks."

Before permitting Adelman to answer, Cranston went on to deplore the thought of "cooperating with a nation that uses nuclear weapons on blacks trying to achieve justice," saying, "It seems to me that we create astounding problems for the United States and Africa, astounding problems at home and so on."

Cranston based his statement on a sentence that hypothesized that if South Africa developed a nuclear bomb it would "gain a deterrent capability with respect to threats it perceives as looming from ground assaults in the region."

When Adelman was given the chance to answer, he pointed out that the study's main finding was that the "overall effect" of South African acquisition of nuclear weapons capability "would be negative" and that the study's recommendation was that "U.S. policy makers try to head off" such an event.

As for Cranston's charge about eventual use of a South African nuclear bomb, Adelman responded: "In all candor, the idea of using nuclear weapons on blacks in South Africa is something that comes as very abhorrent to me personally . . . . It goes against everything I believe in, it goes against everything I have stood for through these years."