A veteran budget analyst says the Patrick administration’s plan to cut the 2010 budgets of executive branch agencies by 8 percent makes sense and would result in a spending reduction of about $1 billion.

Michael Widmer, president of the Massachusetts Taxpayers Foundation, told me he had been expecting cuts in the range of 5 to 10 percent in fiscal 2010, which starts next July. He said those cuts are not likely to be shared equally, since some agencies cannot reduce spending dramatically. The Department of Corrections, for example, cannot just shut down prisons and release inmates.

On Monday, I reported that Gov. Deval Patrick’s secretary of administration and finance, Leslie Kirwan, had told county sheriffs at a meeting that she was asking executive branch agencies to reduce their fiscal 2010 budgets by 8 percent. Kirwan declined comment on the specifics of her presentation, but several other sources who were at the meeting confirmed the 8 percent figure.

Widmer said the executive branch accounts for about half of the state budget, or about $15 billion. He said a reduction in spending is needed to respond to a likely downturn in state tax revenues in the wake of the economic slowdown. Other parts of the budget, including the judiciary, are likely to face budget cuts.

The spending reductions being proposed by Kirwan come on top of a series of cuts proposed to bring this year’s budget into balance. Last month, the governor announced a plan to close an estimated deficit of $1.4 billion by cutting spending and tapping the state’s rainy day reserve fund. Spending cuts totaled more than $900 million, or about 3 percent of the overall $28.2 billion spending plan.