MOSCOW (AP) _ Foreign Minister Eduard A. Shevardnadze said in remarks published Sunday that America's failure to join the Soviet nuclear test ban will affect superpower relations and the summit planned later this year.

Shevardnadze said in an interview with the Mongolian news agency Montsame, as carried by Tass, that the arms control proposal made by Soviet leader Mikhail S. Gorbachev on Jan. 15 should be the focus of his summit meeting with President Reagan.

Shevardnadze returned over the weekend from a tour that included Japan, North Korea and Mongolia.

Gorbachev, in his proposal, said the Soviet Union would extend its five- month-old ban on nuclear testing until March 31, and asked the United States to do the same. The Soviet moratorium was to expire Jan 1.

''If the U.S. Administration takes this new opportunity offered it and stops nuclear weapons tests, this will naturally create a more favorable background for a meeting of the top leaders of the two countries,'' the official Tass news agency quoted Shevardnadze as saying.

''If it does not do so, the atmosphere in our relations will look different, also, specifically, in the aspect of the summit dialogue.''

Shevardnadze is the first Soviet official to suggest publicly that America's failure to join the test ban would affect the summit.

He said steps toward realizing Gorbachev's three-stage plan to rid the world of nuclear weapons by the year 2000 should be agreed at the summit meeting scheduled to be held in the United States. The date has not been set.

''We believe the working out of concrete arrangements on the initial volumes and deadlines of the reduction and elimination of nuclear weapons and other weapons of mass destruction must become the main, central item of the coming Soviet-U.S. summit meeting'' Shevardnadze said.

Tass reported the minister also said Moscow expects a ''constructive and businesslike stand'' on Gorbachev's proposals at the current U.S.-Soviet talks in Geneva, Switzerland, to limit nuclear and space weapons.

He stressed the Soviet view that those talks must link nuclear and space weapons.

''I repeat: These are talks on nuclear and space arms,'' Shevardnadze said. ''The U.S. administration and we have agreed not only on their name but also on the fact that the aforementioned issues will be examined and solved in their interrelationship.''

The United States maintains the talks on limiting nuclear weapons should not include Reagan's Strategic Defense Initiative, or Star Wars, because that project seeks to develop what it says will be defensive weapons.