State Treasurer Timothy P. Cahill says he is considering a proposal to open the state’s $36 billion public employee pension fund to investments by all residents of Massachusetts, after consulting yesterday with the idea’s architect, former US representative Joseph P. Kennedy II.

The proposal is intended to give middle- and low-income families the chance to invest in a fund that is run by top-performing managers and attempts to earn at least 8.25 percent annually. The plan would boost the size of the pension fund, giving the state more buying clout while potentially lowering costs, Cahill said.

“What Joe sees, and what I see, as the real driver here is you could offer top-line investment advice to average workers, which they can’t get on their own,” Cahill said. “That’s the beauty of it. And the diversification [of the pension fund] protects them. Regular people can’t get access to private equity.”

Kennedy said the goal of his plan in simple: Give blue-collar workers and others with moderate wages a chance to make a relatively low-risk investment that would offer the prospect of far higher returns than standard savings or money-market fund accounts.

He contrasted the idea with President Bush’s proposal to create private Social Security investment accounts, which Democrats say could endanger future retirees’ Social Security checks.

Kennedy, who has said he is not planning to run for governor in 2006, unveiled the idea at this state Democratic Party dinner on Monday night and followed up with Cahill yesterday.

If implemented, the Kennedy plan would make Massachusetts the first state pension fund in the nation to open itself up to private investment said Fred Nesbitt, executive director of the National Conference on Public Employee Retirement Systems.

But that’s a big if, he and other pension analysts said.

Fro starters, major investment banks would likely put up a massive fight to such a plan because the Kennedy proposal would essentially make the state pension a mutual fund, said Ed Hennessee, Tennessee’s director of retirement and an officer with the National Association of State Retirement Administrators.

In addition, federal laws may have to be changed to allow such a plan to go into effect, he said. “You can only have in your pension fund public money contributed by employees and employers.”