TORONTO, SEPT. 27 -- Britain's Queen Elizabeth II, still nominally sovereign of Canada as well, approved a request from Prime Minister Brian Mulroney today to add eight new seats to Canada's appointive Senate so the government can ensure passage of a controversial sales tax.

Opponents of the tax immediately cried out in indignation, charging that Mulroney had disgraced the British monarchy by using an arcane provision of the 1867 British North America Act to drag the queen into a partisan conflict.

Some complained that Canada, whose 1982 constitution severed many of the country's formal links to Britain, has returned to a "quasi-colonial status." Many also warned that Mulroney's tactic could exacerbate already deep divisions between the country's English and French speakers.

Opposition leaders in Parliament accused Mulroney of packing the upper house solely to win approval of an unpopular measure, but Mulroney argued that the real issue is the supremacy of the elected House of Commons over the appointed Senate, which is regarded by many Canadians as a wasteful and ineffectual bastion of political patronage. Taking the offensive, the prime minister called the opposition Liberal Party's attempt to use the Senate to block the tax bill a "violation of fundamental democratic principles."

While in Britain the Crown acts as a centralizing force through its still powerful constitutional prerogatives and historic symbolism, in Canada the remnants of its ancient sway tend to have the opposite effect, particularly among the French-speaking majority of Quebec province, which holds little reverence for the monarch of a nation that conquered New France in 1760.

The last time a Canadian prime minister attempted to use a British monarch to alter the makeup of the Senate was in 1874, when a similar request by Alexander Mackenzie was turned down by Queen Victoria. Buckingham Palace gave no explanation for the royal assent to Mulroney's request, which constitutionally can be granted only if there is a deadlock in the Senate on a crucial issue and if it is shown there is no other way to break the impasse.

Liberal Party leader Jean Chretian called Mulroney's action "unbelievable" and predicted that it would be the undoing of the ruling Conservatives, whose approval rating among decided voters has dropped to an unprecedented low of 15 percent, according to a Gallup poll released Wednesday.

Chretian declared that Mulroney could not prove a deadlock existed because the Senate had not yet taken a formal vote on the issue, and he demanded that no new Senate appointments be made until a court has ruled on a challenge to them by the provincial government of British Columbia.

Liberal Sen. Royce Frith, calling Mulroney's move a "completely disgraceful and cynical act," asserted that the prime minister had "seduced the queen for his own political purpose."

The tax measure, the key economic initiative of Mulroney's Conservative government, was approved early this year by the House of Commons. It calls for imposition of a 7 percent value-added tax on virtually all goods and services that government economists have called essential for reducing Canada's mounting budget deficit and reversing a slide toward economic recession.

But with polls showing 80 percent of the population opposed to the tax, the Liberal Party majority in the Senate determined to try to vote down the measure, a step Mulroney charged would cast doubt on the legitimacy of the country's legislative process.

The Senate has not vetoed a money bill in 30 years, and the last time it refused to approve any other government-backed legislation was in 1988, when it balked at passage of the U.S.-Canada free-trade bill. That impasse forced a parliamentary election, in which Mulroney and the Conservatives were reelected.

The Liberals, largely as a result of appointments made by former Liberal prime minister Pierre Trudeau and his Liberal predecessors, had held 52 seats Senate seats to the Conservatives' 46. since then, Mulroney has named 15 Conservative supporters to fill vacancies before seeking to expand the chamber.

As the debate over Mulroney's move heated up, one ambivalent voice was that of John L. Aimers, chairman of the Monarchists League of Canada, a Toronto-based group that promotes loyalty to the British Crown.

"The queen acted absolutely correctly," Aimers said, "but the responsibility for this situation, good or bad, rests squarely on the shoulders of the prime minister. I wish Mr. Mulroney had spared the Crown, which is one of the only unifying things in the country. As a monarchist, I'm really torn. Putting the Crown in that position was unfortunate."