By his own admission, Mayor Michael R. Bloomberg is not the type who is used to taking orders. “It’s been a long time since I’ve worked for somebody,” he said Monday afternoon in Lower Manhattan, after a reporter asked him if he would accept an advisory position with the next president.

“Being an adviser is not something I’m particularly good at,” he went on.

But hardly one to miss an opportunity to weigh in on national politics, Mr. Bloomberg had shared thoughts about how each of the presidential candidates — Senator John McCain of Arizona, the presumptive Republican nominee, and Senator Barack Obama of Illinois, the all-but-certain Democratic nominee — fare on the issue of free trade.

“I think that John McCain has a better record on this issue than Barack Obama,” said the mayor, a free-trade proponent.

And here is how he explained it:

John McCain has spoken out for free trade, for trading with the only ally that we have left in Latin America, namely Colombia. I’ve talked to Senator Obama about this. He assures me that in the end that he is in favor of free trade, although I’d like to hear a lot more from him about how he thinks we could reopen Nafta without coming out a big loser in that.

Fourteen years ago, the United States joined Mexico and Canada to create the tariff-free trade zone known as Nafta, or the North American Free Trade Agreement. The deal has since become a target of intense opposition from labor unions, which blame it and other trade agreements for the loss of American manufacturing jobs.

More recently, free trade became a major issue in the Democratic primaries, as Mr. Obama and Senator Hillary Rodham Clinton of New York battled for votes in Rust Belt states. Then last month, on a trip to Canada, Mr. McCain brought it to the fore again, as he denounced Mr. Obama’s suggestion that Nafta be renegotiated to include stronger labor and environmental standards.

Offering his own opinion, Mayor Bloomberg said that renegotiating Nafta right now was not a good idea. “The fact of the matter is, our trading partners in Nafta would probably want more from us that we want from them,” he explained, responding to no question in particular. “I think, Nafta is a, well, it’s not perfect, but this is certainly not the time to reopen Nafta.”

Free trade was front and center at the afternoon’s event, held outside J&R, the downtown electronics emporium, to mark the start of a five-month, 28-state bus tour that would promote its benefits among average Americans. The tour is the cornerstone of a campaign sponsored by the Consumer Electronics Association, a trade organization that shares the mayor’s position that free trade does not take away jobs, but creates them.

The tour will include stops at the Republican and Democratic conventions, as well as in the nation’s capital, as a means of pressuring Congress to vote on a free-trade deal that the Bush administration has negotiated with Colombia. Mr. McCain supports the agreement as essential to relations with a crucial ally that receives $600 million a year in American aid. Mr. Obama — and many of his fellow Democrats — oppose it, not so much because of workers’ fears of more job losses, but because of concerns about the killings of labor leaders in Colombia.

But let us go back to the mayor, who was once rumored to be interested in pursuing his own presidential bid (and then of being vice president to either party nominee). Though he dismissed the advisory role, Mr. Bloomberg — a longtime Democrat who became a Republican to run for mayor in 2001, and then declared himself an independent last year — said he would be “happy to spend more time with Senator Obama” to discuss the importance of free trade.

And then he added:

I don’t think you can limit free trade and at the same time have better relations with our trading partners. I don’t think you can limit free trade and have control of your borders at the same time. If we don’t support other countries and make sure they have jobs there, their people will come here. And we want to have a balance. We want to have good jobs in both places, and the ways you do that is by enhancing trade.