Former British Prime Minister Edward Heath today accused both Great Britain and the United States of risking global economic collapse by their opposition to adequate economic aid for the Third World.

Heath told a private international monetary conference that the industrial countries in a much-heralded North-South summit in Mexico next October "must agree on an emergency program."

In a press conference following his speech to the bankers, Heath said that so far, efforts to alleviate Third World problems "have been blocked by the Americans and the British." Heath also roundly criticized high American interest rates, a source of more general concern to the financial community assembled here for the conference, an offshoot of the American Bankers Association.

At a private session not open to journalists, Heath said that the U.S. interest-rate policy was based "on a monetarist approach" and on a non-existent free-market mechanism. When challenged from the floor by Richard P. Cooley, chief executive officer of Wells Fargo Bank of Los Angeles, who asked "what would you do instead?" Heath indicated that he would prefer to see the use of a broader name of anti-inflationary instruments rather than monetary policy alone. Europeans reportedly did not join in the Heath-Cooley debate, although American interest-rate policy is widely and publicly criticized here. a

At a separate session on the role of the multilateral institutions, both Abdul Aziz Alquraishi, governor of the Saudi Arabian Monetary Agency, and Cesar Virata, the Phillipines' minister of finance, spoke out strongly in favor of a new energy "affiliate" for the World Bank to finance energy development in the Third World.

Virata said that if the United States continues to oppose the energy affiliate. "It would be contrary to its preaching of supply-side philosophy." aHe said some such mechanism, as well as assistance to the Third World in promoting its exports were vital adjustments for the world's rich nations to make.

Alquraishi predicted that as Iran and Iraq make peace, enabling them to produce more normal supplies of oil, Saudi Arabia will have to reduce its production to avoid a further increase in the world oil glut. He said this combination could quickly wipe out the current Organization of Petroleum Exporting Countries financial surplus because the Saudis' revenues would decline.The implication was that the added revenues for the rest of OPEC would not pile up as surplus reserves, but would be spent quickly for imported goods and services.

The thrust of Heath's remarks was that the Western powers cannot divorce East-West strategic rivalry from North-South economic problems.

Alquraishi also suggested that some of the poorest countries will be easy pickings for "Soviet encroachment" if the West fails to come through with necessary aid. He bewailed the Reagan administration's notion that help on the scale needed can be provided mainly by the private sector. Instead, he argued that the resources of both the IMF and the World Bank must be expanded, increasing at the same time the power of OPEC within the structure of these organizations.

Many of the specific recommendations offered by Heath paralleled the report of the Brandt Commission, of which he was a member. But he buttressed the Brandt Commission generalities by citing the threat to the world economy of potential defaults of $23 billion by Poland and $61 billion by Brazil. London bankers say the Polish debt is in the process of being rolled over. A large loan to Brazil by the IMF is a possibility.

Conference Chairman Roger E. Anderson, who also is chairman of Continental Illinois National Bank and Trust Co. of Chicago, noted that the gap between the rich and poor countries had widened, and had been "aggravated by the oil drain." He said he was saddened to see the needs of the less-developed countries "now and again" neglected by the United States and to hear serious concern for global development dismissed as "part of a Marshall Plan mentality."