Let’s lay out the basics here. Other things equal, public investment is a much better way to provide economic stimulus than tax cuts, for two reasons. First, if the government spends money, that money is spent, helping support demand, whereas tax cuts may be largely saved. So public investment offers more bang for the buck. Second, public investment leaves something of value behind when the stimulus is over.

That said, there’s a problem with a public-investment-only stimulus plan, namely timing. We need stimulus fast, and there’s a limited supply of “shovel-ready” projects that can be started soon enough to deliver an economic boost any time soon. You can bulk up stimulus through other forms of spending, mainly aid to Americans in distress — unemployment benefits, food stamps, etc.. And you can also provide aid to state and local governments so that they don’t have to cut spending — avoiding anti-stimulus is a fast way to achieve net stimulus. But everything I’ve heard says that even with all these things it’s hard to come up with enough spending to provide all the aid the economy needs in 2009.

What this says is that there’s a reasonable economic case for including a significant amount of tax cuts in the package, mainly in year one.

But the numbers being reported — 40 percent of the whole, two-year plan — sound high. And all the news reports say that the high tax-cut share is intended to assuage Republicans; what this presumably means is that this was the message the off-the-record Obamanauts were told to convey.

And that’s bad news.