WASHINGTON—Deficit-reduction measures and an overhaul of the tax code—not more federal stimulus—offer the best solutions for bolstering a still-struggling economy and bringing down the high unemployment rate, two former Treasury secretaries said on Sunday.

Former Clinton Treasury head Robert Rubin, appearing on CNN's "Fareed Zakaria GPS," said a second major stimulus package, such as that passed by Congress last year, could be "counterproductive," further undermining confidence in an economic recovery he described as "slow and bumpy." Instead, Mr. Rubin said, policy makers should begin crafting a deficit-reduction plan that would go into effect by the end of President Barack Obama's first term.

"If you could do it and it was credible and people believed it and it was real, I think that could do a lot for confidence," Mr. Rubin said.

Paul O'Neill, who helmed the Treasury under former President George W. Bush, said he supported allowing Bush-era tax cuts to expire. The issue has become a political football for Democrats and Republicans ahead of November's mid-term elections. Mr. O'Neill said that instead of focusing on which tax breaks should be allowed to expire, the White House should push for more, wholesale changes to the tax system.

"I think that would give reassurance to the markets that we're coming back and we're creating the basis for capital formation and ... savings as opposed to consuming everything in sight," Mr. O'Neill told CNN.