What’s the difference between natural and national? A lot, actually.

The Natural Resources Defense Council is one of the country’s largest environmental groups with 1.3 million members, an annual budget of $95 million and a staff of some 300 lawyers, scientists and policy experts who bring pro-environment lawsuits around the country.

Except that The Post, in a Business section story Sunday about the new kinds of energy-saving light bulbs, called it the National Resources Defense Council — twice, in the story and in the factoid pull-out graphic. Ouch.

This mistake may seem minor in the grand scheme of things. But in the context of this town, it is almost unforgivable. The words are similar enough, sure — natural and national — but if you’ve spent any time in D.C., you know that the NRDC is about natural resources, not national resources. You practically can’t do any story on energy or the environment in this city without encountering NRDC. Its name should be on a basic copy editing test for anyone working at The Post.

Greg Schneider, national economy and business editor, said the mistake was in the original story from freelancer Paul Glader, a former Wall Street Journal writer now based in Berlin. Glader is a pro, and he made the error. But the mistake also escaped a Post business desk editor, and then a copy editor.

Copy editors say the Business desk had a lot of late copy Friday night for the Sunday print edition. There is only so much time that editors can take with each story when they are overwhelmed.

This one was published online Friday with the errors, appeared in Sunday’s print edition, still containing the errors, and was finally corrected online Monday and in print Tuesday.

It’s maddening, and these kinds of mistakes happen all too often in The Post. And it’s more maddening when Edwin Chen, federal communications director for NRDC, a former White House reporter for Bloomberg and the Los Angeles Times, has to e-mail on a Sunday and tell you about it, which he did to me and other Post editors.

Ed is a past president of the White House Correspondents’ Association and one of the straightest shooters in this town. As Ed puts it, getting his organization’s name wrong, is “an all-too-common occurrence.”

I don’t mean to pile on, but copy editing mistakes are among the most frequent complaints to the ombudsman. Here’s a recent letter I received from a former Post staffer who asked for anonymity to not offend former colleagues. This person remains a loyal but frustrated reader:

“I have been reluctant to write this e-mail. But I can no longer hold my tongue. The quality of copy editing at the paper is abysmal. Yet again, while reading a story, I have found another error — a ‘they’ where it should have read ‘the’ — that literally made me stop reading the story and write this e-mail.

“Unfortunately, it’s not a rare occurrence — countless stories and blogs with words left out or misspellings or grammatical errors. Is anybody reading what goes on up on the Web site or in the paper?

“I know firsthand the troubles of the newspaper industry — particularly at The Washington Post, where buyouts have diminished a once-robust staff. I understand that there are fewer copy editors reading more copy, especially the ridiculous amount of blogs that currently consume the Web site. But the copy errors are a problem that points to an internal quality-control issue. In addition, it diminishes the overall reputation of the paper. Something has to be done internally to raise the level of copy editing at the paper.

“Thanks for allowing me to vent.”

I didn’t get an on-the-record response from the copy desk to the former staffer, but I know from past conversations with senior copy editors that these are some of the problems:

First, mathematics is at play here: Fewer editors plus much more copy equals more mistakes. The Washington Post is not just a print publication anymore — far more copy, from stories to blogs, exists online than in print. The print edition is a fraction of what editors edit every day.

Second, copy editors (multiplatform editors, in today’s parlance) also now deal with material for mobile devices and tablet computers. Each of these four platforms — print, online, mobile, tablet — has different procedures and may require distinct headlines and captions; a story can be prepared by the copy editor not once but four times.

Third, mistakes occur more frequently online than in print, generally, because online copy goes through fewer editors. Stories headed into the newspaper go through more editors. But online errors are easier and faster to correct. Print is still forever. Readers take mistakes in print more seriously than online errors.

I concur with the former staffer. Something has to be done to shake up the copy editing system at The Post so it doesn’t let mistakes like this weekend’s get published. It’s too important to the credibility of The Post.