Treasury Secretary Lawrence H. Summers offered a detailed critique of Texas Gov. George W. Bush's Social Security plan yesterday, wading into a political fight usually shunned by his predecessors and creating an unusual chorus of criticism of the GOP presidential nominee by senior Cabinet officials.

In an interview, Summers said that Bush's comments on Social Security "reveal a fundamental misunderstanding of the system." The Bush plan to divert a portion of payroll taxes to help establish individual accounts for young workers, he added, will require either "large cuts" in guaranteed benefits or an infusion of billions of dollars in new revenue.

But Summers--an economist who also serves as managing trustee of Social Security and conducted academic work on funding the system before he entered government--said there is no way money collected now can also pay current benefits if it is channeled into investment accounts.

"It is an arithmetic challenge that cannot be met," Summers said, asserting that under the Bush plan the Social Security trust fund would be fully depleted when someone who is now 42 retires.

Summers's remarks come as the Gore campaign and the Democratic National Committee are pounding battleground states with advertisements and recorded phone calls that echo the themes outlined by Summers--that Bush's math on Social Security doesn't add up and that the Republican is bound to break promises to either senior citizens or young workers.

While Summers is a key behind-the-scenes economic adviser to Vice President Gore, the Treasury secretary, the secretary of state, the defense secretary and the attorney general are generally the Cabinet officials who try to remain aloof from politics in presidential elections.

Yet, over the weekend, Secretary of State Madeleine K. Albright also departed from that tradition, taking the unusual step of denouncing Bush's proposal to withdraw U.S. ground forces from the Balkans as risky and misguided and possibly leading to the dissolution of NATO.

"This is a very inappropriate continuing pattern of the politicization of the most sensitive Cabinet agencies, State and Treasury," said Bush spokesman Ari Fleischer. "In the waning days of the Clinton era, perhaps it was too much to hope that the historically nonpolitical agencies could remain above the fray."

As Treasury secretary four years ago, Robert E. Rubin would only obliquely make observations about the economic proposals offered by Republican presidential candidate Robert J. Dole, usually in response to questions and then mostly to defend administration policy. Nicholas Brady, Treasury secretary in 1988 under President Ronald Reagan and in 1992 under Bush's father, President George Bush, said yesterday that Summers's comments were "totally inappropriate."

"I don't think it's his business to be commenting on Governor Bush's proposal on Social Security," Brady said.

Allen Sinai, chief executive of Primark Decision Economics, agreed that the critique was unusual but said it was appropriate, given Summers's background. "We happened to have the coincidence of having a Treasury secretary who is also the finest economist of our generation," Sinai said. "Who's to say what's fair or not fair?"

Treasury officials made much the same case, saying Summers's comments were justified because he is the managing trustee of Social Security and had been considered an expert in the field when he was in academia.

Summers also took issue with Bush's claim that he would be able to build up $3 trillion in these new private accounts while also eliminating the national debt by 2016. Gore has set a goal of eliminating the debt by 2012.

"Without dedicating Social Security surpluses to debt reduction rather than to new private accounts, it appears to me that on any realistic basis it is impossible to eliminate the debt any time in the next 20 years without using nearly the entire budget surplus, which is clearly precluded by their large tax cuts," Summers said.

Under the Bush plan, about $1.9 trillion would be transferred from the Social Security surplus to the private accounts by 2016, which the campaign says would grow to $3 trillion, assuming a 5.5 percent return and moderate inflation. But that money could not also be used to pay down the debt.

Fleischer insisted the Bush plan will pay down the entire national debt by 2016.

Summers began making the case against Bush's Social Security plan in a little-noticed address before the Conference Board in New York last week. In that speech, he said that diverting two percentage points of the payroll tax--about 15 percent--a year "would lead to an excess of benefits over tax revenues by 2005, and the total exhaustion of the trust fund in the early 2020s."

Yesterday, Summers expounded on that theme and also targeted Bush's contention in his first debate with Gore that "I want to get a better rate of return for your own money than the paltry 2 percent that the current Social Security trust gets today."

Summers said that reflected a "fundamental misunderstanding" because payroll taxes are used to provide benefits for retirees, the disabled and survivors, and thus can't be invested. "Comparing rates of return is just not a legitimate argument," Summers said.