Secretary of State Cyrus R. Vance said yesterday that neither the Soviet Union nor the United States has altered its position on strategic arms limitations since the breakdownof negotiations during the March trip to Moscow.

Vance said there had been no new proposals by either side in preparation for his May 18 Geneva meeting with Soviet Foreign Minister Andrei Gromyko and declined to discuss the prospects for progress at that meeting.

In addition to discussing arms limitation, Gromyko and Vance will talk about the Middle East and sign a treaty renouncing modificationof the environment.

On other subject, Vance told a State Department press conference.

He expects to visit the Middle East after a new government is formed in Israel. The administration still believes it is important to convene a Geneva meeting on the Mideast this fall, and will have suggestions "on all the core issues" - the Palestinians, the return of territory to the Arab states and a definition of peace.

The United States is unalterably opposed to South Africa's policy of racial sepration (apartheid), and Vice President Mondale will aks South African Prime Minister John Vorster at their May 14 Vienna meeting what steps South Africa is taking to move away from apartheid.

He will meet Rhodesian black leader Joshua Nkomo in London Friday and expects that a joint British-American plan aimed at achieving majority rule peacefully in Rhodesia will be completed by mid-May.

Human rights remain "absolutely central to our foreign policy." He rejected a suggestion that the administration was moderating the fervor of its advocacy of human rights.

The administration is watching developments in Ethiopia's Somalia and Djibouti very closely and has completed a new study of the area. "Recently the situation has become more tense," he added.

The United States hopes that the European summit to which President Carter is to fly today will bring greater support for the International Monetary Fund and joint approaches on trade, energy and economic problems.

"It is indeed a difficult problem," to move toward nomalization of relations with China, and he still hopes to make a trip to China late this year to examine the subject in detail. China is pressing Washington to move toward normalization more swiftly.

Published reports that Paul C. Warnke, director of the Arms Control and Disarmament Agency, softened the U.S. strategic arms proposals during the March negotiations with the Soviets are not true. The secretary said it was nto Warnke who orginated the proposal that cruise missiles with a range of over 600 kilometers be barred from all but the largest bombers. The proposal. Vanc esaid, was designed primarily to limit the capabilities of the Soviet Backfire, which is a medium-sized bomber. Some press reports have portrayed it as a concession to the Soviets.