In the strongest denunciation of British Prime Minister Margaret Thatcher's monetarist economic policies by a senior member of her Conservative Party, former prime minister Edward Heath today launched a public campaign to try to force her government to change course.

"It is imperative in our present economic circumstances, both national and international, that we should make a completely fresh assessment of Conservative economic policy," Heath said in a speech in Manchester that attracted wide attention here.

"Many of us have remained almost silent for a long time on these matters, perhaps for far too long, in order that the dire consequences of the present dogmatic policies could be more widely recognized," he said. "We were hoping that they would bring about a more pragmatic approach to economic affairs."

Heath said the recent increase in minimum interest rates from 12 to 16 percent, "the still further increase in unemployment and the numbers of liquidations which are bound to follow, the rise in mortgage rates together with the hardship and personal bankruptcies associated with them all indicate that the situation is getting worse, not better, and that the policy has become more dogmatic, not less so."

Heath, who was replaced by Thatcher as Conservative Party leader after national election defeats in 1974, told reporters he was not seeking to depose her but to stir debate within the party about her policies. Despite his international standing, he has little remaining personal following even among her other critics in the Cabinet or on Conservative back benches in Parliament.

But his outspoken opposition to Thatcher's policies, which he intends to press in more speeches this week and during the Conservatives' annual party conference next week, could damage Thatcher's prestige and embolden more critics.

Heath did not completely detail his proposals today, but he said they would be built on a drastic reduction of interest rates here and in the rest of Europe, whether or not U.S. interest rates, which helped force the others up, are reduced.

Both Britain and the Conservative Party were being hurt, Heath charged, by the abandonment of postwar "consensus" politics, which he defined as "deliberately setting out to achieve the widest common measure of agreement about our national policies, in this particular case about our economic activities, in the pursuit of a better standard of living for our people and a happier and more prosperous country."

Thatcher, who is in Australia at a Commonwealth prime ministers' meeting, responded to this in remarks she added to a speech at the University of Melbourne today. "For me," she said, "pragmatism is not enough, nor is the fashionable word 'consensus.' For me, consensus seems to be the process of abandoning all beliefs, values and qualities."