President Barack Obama’s budget proposal would be “marginally positive” for U.S. credit ratings in the short term, but there is “almost no chance” Congress will pass the plan as it was presented, Reuters said after a report today from Moody’s Investors Service.

In the long run, the budget proposal fails to address key structural issues such as entitlement programs, Moody’s senior analyst Steven Hess said in the report. Some of the plan’s projections also are questionable, he said.

“These uncertainties, combined with the continued, elevated levels of debt, indicate that additional measures would be required to improve the government’s finances and debt position over the long term,” Hess said.

Moody’s, which has recently warned about the rising likelihood of a negative outlook on the nation’s triple-A rating, noted that the estimated budget deficit of 10.9 percent of gross domestic product for this year represents the largest shortfall since World War II, resulting from the extension of the tax cuts introduced by former President George Bush.

It is still an open question, however, whether the government will raise taxes for high-income earners after 2012, when the tax cuts expire, Moody’s said.

The agency also raises questions about some of the projections included in the current budget proposal, in particular for non-security discretionary spending, which is forecast to be 11 percent lower in nominal terms by 2021.

“Such an extended period of no-growth in nominal spending would be unprecedented,” Hess said. “The feasibility of such a large, prolonged decline in discretionary spending is highly questionable.”