For Reagan administration officials, the new hot-line agreement with Moscow has political as well as military and diplomatic importance. At a time when the President is trying to prove his good intent on arms control, this upgrading in US-Soviet communications facilities - which came at the invitation of Washington - is a timely reminder that the administration is willing to talk with its Soviet adversary if not be more accommodating.
Yet this small but significant step for nuclear sanity also points up certain shortcomings in the agreement's details as well as future political challenges for the President on the war-and-peace issue.
The administration has been accused of developing a nuclear ''warfighting'' policy; that is, planning how to conclude an atomic exchange on the most favorable terms rather than simply assuming that any nuclear war would wipe out civilized society.
Under pressure from nuclear-freeze advocates as well as Congress, the Pentagon developed and the President approved this new effort to reduce the threat of superpower confrontation.
But the hot-line accord - while welcomed by all concerned - falls short of what thoughtful lawmakers of both political parties want.
Democratic Sens. Bill Bradley of New Jersey and Sam Nunn of Georgia, together with their Republican colleague John Warner of Virginia, continue to push for ''risk reduction'' or ''crisis'' centers that would greatly expand existing hotline facilities. Facilities of this kind in superpower capitals become increasingly important, they warn, as more third world countries attain nuclear technology and the threat of inadvertent war or nuclear terrorism increases.
In recent weeks, the Republican-controlled Senate has unanimously approved resolutions that would call on the President to establish such centers. The Bradley proposal is part of the 1985 defense authorization bill now in House-Senate conference (as is a little-noticed provision to establish a controversial ''Peace Academy'').
Late last year, a ''Working Group on Nuclear Risk Reduction,'' including former senior military, intelligence, and arms-control officials, warned Senators Nunn and Warner of ''an increasing number of circumstances that could precipitate the outbreak of nuclear war that neither side anticipated nor intended, possibly involving other nuclear powers or terrorist groups.''
Senator Bradley, announcing his nuclear crisis center resolution earlier this year, said: ''The future of the world as we know it could depend on instantaneous communications between the United States and the Soviet Union.''
Bradley's proposal features round-the-clock staffing of facilities that would include voice and teleconferencing capabilities as well as the new facsimile hotline for printed documents, pictures, and maps. The New Jersey Democrat suggests assigning an American liaison officer to the center in Moscow with a Soviet counterpart in Washington.
Such facilities would be similar to those shown in the film ''Fail-Safe'' 20 years ago.
They would provide far more than will exist under the improved hot line, which does not include telephonic exchanges or the ability for Soviet and American military officers to communicate directly.
Some experts think world leaders should be able to talk to each other during times of crisis.
But in outlining the hot-line improvements a year ago, the Pentagon concluded that voice communications are ''far more subject to misunderstanding'' and could ''encourage instant response, thereby denying the head of state the necessary opportunity to consult with advisers and prepare a thoughtful and measured response.''
Part of the problem is Soviet intransigence. While Moscow wants to continue pursuing new channels of communication for potential nuclear terrorist episodes, it has so far refused to consider direct military-to-military communications facilities or improved contacts between embassies and foreign ministries.
Yet, mindful of the administration's arms control image, senior White House officials call the improvements in communications facilities announded this week ''a step in arms control.''
''It is not an agreement that limits the number of weapons,'' said a senior administration official. ''But it fits into the area of confidence-building measures.''
The connection between this new accord and the touchy subject of space weapons is clear.
The new high-speed transmission system will rely on satellites to prevent misunderstanding during times of crisis. The administration needs to show progress on limiting antisatellite weapons if it is to win congressional approval for new ASAT testing.
But it is far from certain that the Soviet-proposed talks in Vienna tentatively scheduled for September will occur. Senior officials insist that the US will be in Vienna ''without preconditions.'' But they still say that space weapons discussions cannot fail to consider ballistic missiles, which are weapons that pass through space, make use of satellites, and include technology similar to that envisioned for more exotic ''Star Wars'' systems.