Let's stipulate, up front, that there's plenty of blame to go around on Katrina.

Two years ago this week, and ever since, a Republican president, a Democratic governor and a Democratic mayor all have seemed to be competing for the prize of "most incompetent." Also, let's just say it and get it out of the way: During the hurricane, and in its aftermath, some of the people of New Orleans didn't acquit themselves very well either.

But the real lesson of Katrina is for all of us everywhere: The physical environment matters — a lot more than we have been willing to acknowledge, or pay for.

And when I say "physical environment" I don't mean polar bears and penguins. I mean the environment right around us — our surroundings defined by fire hydrants and roads, ports and airports, levees and walls.

Yet, for decades now, both the political left and the political right have chosen to scrimp on infrastructure.

For the left, the anti-infrastructure backlash started with the environmental movement. Once upon a time, New Deal Democrats were eager to pour concrete and build dams; it was jobs for workers and votes for the party of Franklin D. Roosevelt.

But starting in the '70s, the greens gained sway in the Democratic Party. Today, there's not a place in this country where eco-activists and litigators haven't blocked construction of a highway or a bridge.

For its part, the right has changed its tune, too. The Federalists of Alexander Hamilton, the Whigs of Henry Clay and the Republicans of Abraham Lincoln all were proponents of "internal improvements" — turnpikes, canals, railroads. And even as a young Army officer, Dwight D. Eisenhower could see that America needed good roads to move troops around; it was a national-security issue. So when Ike, a Republican, became the 34th president, he spearheaded the Interstate Highway System.

But starting in the '80s, a new, more libertarian attitude took hold in the Republican Party. Ronald Reagan's main domestic focus was tax cuts and spending cuts, and infrastructure spending was easier to reduce than Social Security. To an avant-garde Reaganite, federal money for infrastructure was just pork-funding for unionized workers and entrenched political machines. The better approach? "Starve the beast" by cutting spending.

And besides, the new logic continued, "public works" should be privatized works. In other words, let the market decide if we need , say, a new port — and who should own it.

Then came the Internet. The whole notion of the physical world seemed to be challenged by the newer notions of cyberspace and virtual reality. At a time when Microsoft and Google were remaking the future online, who wanted to worry about boring old bridges in Minnesota or levees in New Orleans? The big issues in D.C. think-tank conversation, left and right, were spectrum and Wi-Fi, not asphalt and waterworks.

And so, undermined by both parties, federal spending for infrastructure collapsed — from a high of 1.17 percent of gross domestic product in 1980 to less than half that today.

Yet, the past few years have reminded us that although infrastructure might not be trendy, it's as important as ever. The starkest illustrations, of course, were 9/11 and then Katrina — either we are safe in our cities, or we're not. Either we can defend our borders against all kinds of threats and evacuate our populations if need be, or we can't.

Meanwhile, evidence of our underinvestment continues to mount. On Friday, USA Today reported that suburban sprawl has spread faster than firefighters' ability to locate fire hydrants in new housing developments; one- quarter of all houses are thus at risk. Having a BlackBerry won't help if the hose won't reach your house.

If both parties got us into this hole, then both parties will have to dig us out. It will be expensive — but we're worth it.

James P. Pinkerton is a Newsday columnist. Reach him at pinkerto@ix.netcom.com.