Mary Rosh thinks the world of John R. Lott Jr., the controversial American Enterprise Institute scholar whose book "More Guns, Less Crime" caused such a stir a few years ago.

In postings on Web sites in this country and abroad, Rosh has tirelessly defended Lott against his harshest critics. He is a meticulous researcher, she's repeatedly told those who say otherwise. He's not driven by the ideology of the left or the right. Rosh has even summoned memories of the classes she took from Lott a decade ago to illustrate Lott's probity and academic gifts.

"I have to say that he was the best professor I ever had," Rosh gushed in one Internet posting.

Indeed, Mary Rosh and John Lott agree about nearly everything.

Well they should, because Mary Rosh is John Lott -- or at least that's the pseudonym he's used for three years to defend himself against his critics in online debates, Lott acknowledged this week.

"I probably shouldn't have done it -- I know I shouldn't have done it -- but it's hard to think of any big advantage I got except to be able to comment fictitiously," said Lott, an economist who has held senior research positions at the University of Chicago and Yale.

Moreover, the AEI resident scholar acknowledged on Friday that he permitted his 13-year-old son to write an effusive review of "More Guns, Less Crime" and then post it on the Web site. It was signed "Maryrosh."

His son gave the book five stars -- the highest possible rating.

"If you want to learn about what can stop crime or if you want to learn about many of the myths involving crime that endanger people's lives, this is the book to get," the review stated. "It was very interesting reading and Lott writes very well. He explains things in an understandable commonsense way. I have loaned out my copy a dozen times and while it may have taken some effort to get people started on the book, once they read it no one was disappointed."

Lott denied that he was the author of the review, an assertion made on various Web sites that have been tracking the controversy. He said his son wrote it, with some help from his wife. "They told me they had done it. They showed it to me. I wasn't going to tell them not to do it. Should I have?"

Lott's book, which argues that gun ownership deters crime, has been praised by gun advocates and attacked by those who favor gun control.

Lott also is a lesser player in the now-diminishing debate over the 2000 elections. In a study two years ago, Lott reported that the decision by the major television networks to call the Florida election for Al Gore before the polls had closed everywhere in the state led thousands of Republican-leaning voters in the Florida Panhandle not to vote. Other researchers dispute his findings, which have been embraced by conservatives as well as by critics of exit polling.

Lott said that he frequently has used the name "Mary Rosh" to defend himself in online debates. The name is an amalgam of the first two letters of his four sons' first names. In a posting to the Web site maintained by Tim Lambert, an Australian professor who has relentlessly attacked Lott's guns studies, "Mary Rosh" claims to be a former student of Lott at the University of Pennsylvania, where the economist taught between 1991 and 1995.

"I had him for a PhD level empirical methods class when he taught at the Wharton School at the University of Pennsylvania back in the early 1990s, well before he gained national attention, and I have to say that he was the best professor that I ever had. You wouldn't know that he was a 'right-wing' ideologue from the class. . . . There were a group of us students who would try to take any class that he taught. Lott finally had to tell us that it was best for us to try and take classes from other professors more to be exposed to other ways of teaching graduate material."

When a reporter attempted to read the posting to him over the telephone, Lott stopped him after the first few words. "I'm sure I did that. I shouldn't have done it."

Julian Sanchez, a Cato Institute staffer, is the cybersleuth who tracked Mary Rosh back to John Lott.

Sanchez is a blogger -- someone who maintains a Web site where they report and comment on the news -- who had been tracking the debate between Lott and critics of his gun research. He became suspicious about Rosh after he noticed that several of Rosh's online defenses of Lott seemed to track closely with arguments the scholar himself had made in private e-mails to Sanchez and other bloggers. He tracked Mary Rosh's IP address (the computer code translation of the standard e-mail address) to Pennsylvania.

"I compared that IP with the header of an email Dr. Lott had sent me from his home address. And by yet another astonishing coincidence, it had originated at the very same IP address. Now, what are the odds of that?" he wrote in a posting on his Web site. "Sarcasm aside, we're a little old to be playing dress up, aren't we Dr. Lott?"

Lott said he initially used his own name in online debates with critics. "But you just get into really emotional things with people. You also run into other problems." So he started using the name Mary Rosh. "I should not have done it, there is no doubt. But it was a way to get information into the debate."

Officials at the American Enterprise Institute declined to comment yesterday.

John R. Lott Jr. signed a copy of "More Guns, Less Crime" in February 2000 in Westminster, Md.