A commission including members of Congress from both parties is proposing a sweeping plan to shore up Social Security, calling for the establishment of personal investment accounts and a gradual increase in the retirement age to 70.

The report Tuesday is the most comprehensive package of recommendations to date for remaking Social Security in preparation for the baby-boom generation's retirement. It says the changes would keep Social Security solvent for at least 75 years without raising taxes, even as it trades some reductions in guaranteed benefits for the higher if less certain returns of the financial markets.Prepared after 15 months of study by the National Commission on Retirement Policy, a private group of lawmakers, economists, pension-system experts and business executives that was assembled by the Center for Strategic and International Studies, the report is likely to wield considerable influence at the White House and on Capitol Hill as Democrats and Republicans seek solutions to one of the most politically sensitive issues facing the nation.

While the committee's main recommendations are sure to be hotly debated, the report underscores the speed with which once-radical options for Social Security, like the addition of an investment component, have become part of the political mainstream.

Powerful interest groups including the American Association of Retired Persons oppose creating private accounts within the Social Security system, as do many liberal Democrats.

While the congressional Democrats and Republicans on the commission backed the investment-oriented approach, the panel had no members drawn from labor unions or other groups that have fought to maintain Social Security as a guaranteed safety net against poverty and old age.

But with the stock market booming and many people more comfortable than even a few years ago with investing on their own, Democrats including Sens. Daniel Patrick Moynihan of New York and Bob Kerrey of Nebraska have joined many Republicans in backing private accounts.

"This report brought together people who really understand the issue," said Sen. Judd Gregg of New Hampshire, a Republican and a co-chairman of the commission. "It's bipartisan. It's the only plan out there scored by Social Security's actuaries as saving the system for the next century. And it says it can be done without raising taxes or significantly impacting people in a negative way."

The report was unanimously approved last week by the commission's 24 members, including Sen. John Breaux, D-La., and Reps. Charles Stenholm, D-Texas, and Jim Kolbe, R-Ariz. Breaux, Stenholm and Kolbe were co-chairmen of the commission, along with Donald Marron, chairman and chief executive of Paine Webber Group, the Wall Street firm, and Charles Sanders, former chairman of Glaxo Inc., the pharmaceutical company.

Marron said the proposal should play a central role as Congress and the White House move toward drafting Social Security legislation next year.

"Unlike other proposals this one has a great degree of detail and a focus as far as turning it into legislation," Marron said.

The report calls for diverting into personal investment accounts 2 percentage points of the 12.4 percent payroll tax levied on workers and their employers to finance Social Security. The change, which would not affect current retirees, would allow individuals a choice of investment options for the money accumulating in their government-administered accounts, including stock-index funds and treasury securities.

Since allocating a portion of payroll tax receipts toward investment accounts for current workers would eventually leave the retirement system short of the money needed to pay benefits to current retirees, the report calls for the government to make up the difference with the federal budget surpluses projected for coming years.

But the plan also calls for a number of other steps to reduce the financial strain on Social Security as the 76 million baby boomers born from 1946 through 1964 start heading into retirement a decade from now.

The retirement age, which is already scheduled to rise to 67 from 65 over the next few decades, would rise under the commission's plan to 70 by 2029. The early retirement age would rise to 65 from 62 by 2017.