The North Atlantic Treaty Organization formally endorsed today the U.S.-Soviet talks in Geneva next month and expressed hope that the meeting will lead to "equitable, verifiable and balanced agreements" for reducing nuclear weapons.

Foreign ministers of the 16-nation alliance ended a harmonious meeting here by welcoming the talks on Jan. 7 and 8 between Secretary of State George P. Shultz and Soviet Foreign Minister Andrei Gromyko "on the whole range of questions concerning intercontinental and intermediate-range nuclear weapons and arms in outer space."

NATO's goal, the ministers said in a communique, is to ease East-West tensions and substantially reduce nuclear weapons through U.S.- Soviet agreements "in which all concerned can have confidence."

At a news conference, Shultz said his fellow ministers had counseled him "to show patience and to go to Geneva without illusions about the difficulty of that task." He added:

"I am going there prepared for serious, substantive discussions. From all I can tell, the Soviet Union is similarly preparing itself. Then we'll just have to see what comes of it."

Shultz reiterated that the Reagan administration intends to consult with its allies as he prepares for the Gromyko meeting, and added, "After the talks in Geneva, whatever the outcome, we will take steps to see that our allies are informed."

He said that would be done at a special meeting here of the full NATO membership and by visits to the capitals of each member country. He did not elaborate, but senior U.S. officials said the task of informing the allies probably will be entrusted to an emissary such as Paul A. Nitze, who has been named a special adviser to Shultz on arms control.

Shultz said the allies are particularly interested in how U.S.-Soviet negotiations will affect NATO's controversial 1979 decision to deploy 572 American-produced, medium-range cruise and Pershing II missiles in Western Europe.

The first deployments last year in Britain, West Germany and Italy caused the Soviets to walk out of earlier arms control talks in Geneva. As a spur to gaining renewed Soviet cooperation, the communique restated NATO's "two-track policy" of offering to reconsider the deployments in Western Europe if the Soviets reduce their SS20 missiles in Eastern Europe. It said:

"The allies concerned are willing to reverse, halt or modify the longer range INF intermediate nuclear forces deployments -- including the removal and dismantling of missiles already deployed -- upon achievement of a balanced, equitable and verifiable agreement calling for such action." But it also warned: "In the absence of a concrete negotiated result obviating the need for such deployment, the allies concerned emphasized their determination to continue the deployment of longer range INF missiles as scheduled."

However, as they have in the past, two countries formally reserved their position on that portion of the communique. They were Greece, where the government of Prime Minister Andreas Papandreou is hostile to deployment, and Denmark, where the government is susceptible to pressure from antinuclear forces.

Two other members, Belgium and the Netherlands, each of which is supposed to deploy 48 cruise missiles, also have been forced by domestic opposition to delay deploying the missiles. But, in what U.S. officials interpreted as an encouraging sign, both governments endorsed today's communique language reaffirming the two-track policy.

At his news conference, Shultz was asked about whether the United States intends to press ahead with President Reagan's "Star Wars" proposals for developing and testing outer space weapons. That plan has been opposed vehemently by the Soviets and also has stirred concern among West Europeans who are fearful of its implications.

In response, Shultz described Reagan's plan as "a research program," and he said, "I think it is a very positive contribution to strategic deterrence." When questions persisted about whether the United States might delay testing of anti-satellite weapons, he replied, "How can you delay a research program?"