IT'S increasingly clear: The Reagan administration is gearing up to negotiate some kind of arms control agreement with the Soviet Union. And it would be profoundly unfortunate for a domestic Maginot Line of distrust of Soviet motives and intentions to rip out the underside of US efforts.
Certainly Margaret Thatcher, the world leader along with Japan's Yasuhiro Nakasone closest to Mr. Reagan, has gone out of her way to give Mikhail Gorbachev a stage on which to present the Soviet case. We should not miss such pointed encouragement from American allies to speed the talks progress along.
The stylish, youngish Gorbachev represents a more attractive Soviet face to show the West at this crucial time, three weeks before the scheduled start of talks between Secretary of State George Shultz and Andrei Gromyko in Geneva. Certainly Gorbachev exudes more of an air of approachability than would other leaders from the stolid lineup of Soviet technocrats. Few dispute that his short list of Soviet arms concerns is what worries Moscow most: American defensive weapons in space and imminent testing of antisatellite weapons.
Gorbachev's London themes were a familiar blend of openness and toughness: ''I would like to stress once again that the Soviet leadership stands for forthright and honest talks to help us, on a mutually acceptable basis, limit and reduce arms, primarily nuclear weapons, and eventually eliminate them. We are ready to go here as far as our Western partners in the talks. Naturally enough, equality and equal security shall underlie any agreements in this field. And, of course, any course that seeks military superiority over the USSR and its allies is unacceptable and has no prospects.''
One line of reaction in the United States is to argue that the Soviets are not to be trusted, period. Followers of this line would discount anything favorable in Gorbachev's London appearance, or indeed anything in the very broad range of US-Soviet relations that might lull a naive American public and government into a dangerously false peace. Such a wariness has its uses.
But a president has to decide for himself whether to move ahead, or to attempt to stand pat with a strategic relationship that is itself rapidly and dangerously shifting. Cynicism itself can corrode the prospects for peace.
If Mr. Reagan reaches an arms accord with the Soviet Union, he will do it his own way. The setting, approach, and result will be unlike anything before it, including Richard Nixon's and Jimmy Carter's encounters with Leonid Brezhnev.
In the broad range of ties, including the current naval manuevers in the Far East, there's an evident edginess about potential confrontation with the Soviets. At the same time, Defense Secretary Caspar Weinberger got a Reagan initial this week for all the defense dollars he could hope to chew on next year. Despite the grousing about ''verifiability'' of agreements, by the end of next year Washington may be saying it can verify compliance.
And with this week's announcement of a January space shot, reportedly to launch a verification satellite for scrutinizing Soviet territory, the Department of Defense may be protesting too much about disclosure. What could be nearer the hearts of those most fretful over Soviet reliability than a verification satellite?
By appointments and staff pruning, the administration has been attempting to contain the internal network that opposes arms control and to create a new lineup to take advantage of any genuine opportunity.
The significant Gorbachev meetings in London with archly receptive British hosts bring American allies clearly into the picture. Some of those allies, such as West Germany, have their own concerns about American arms advances. The ambitious US space defense program affects NATO strategy in ways not yet acknowledged. And allies see space defense programs as subsidizing the US high-tech industry.
Mr. Reagan, in his second term, appears to be giving the attention to superpower relations and arms control that he gave to congressional relations and budget cutting his first term. If this is so, he should be encouraged to grasp the moment and succeed in foreign affairs as he proceeded on the domestic front.