Mayor Bloomberg’s announcement that the city is hosting this year’s annual Farm Aid concert suggests that he has moved beyond New York City voters and is trying to appeal to a more national audience.

The event, which will take place on Randalls Island in September, is already giving the mayor a platform to talk about the importance of family-owned farms, a concern that is not at the top of most New Yorkers’ lists.

Mr. Bloomberg said yesterday that New York might not immediately spring to mind as a logical venue for Farm Aid, but he made the case for bringing the concert to the city, saying it will generate nearly $13 million of economic activity and further boost area farmers, who sell their produce at a growing number of green markets here.

“Two years ago, many asked the same question as to why New York was the proper venue when we brought the Country Music Awards here,” the mayor said during a news conference with the cofounders of Farm Aid, Willie Nelson and John Mellencamp, in Union Square. But he said that as counterintuitive as it sounds, New York State is the second biggest country music market in America and a “great agricultural state.”

Pollster Scott Rasmussen said the Farm Aid concert is something that could be useful for Mr. Bloomberg to tout when he travels the country to places such as Missouri, where he is scheduled to speak at a conference next month.

“If the mayor is trying to keep people thinking that he is thinking about running for president, it’s a perfect event,” Mr. Rasmussen, who is releasing a poll this morning that matches Mr. Bloomberg against Democratic and Republican presidential candidates in New Jersey, said. The mayor has denied his candidacy in the past.

The Farm Aid event was part of a package of initiatives Mr. Bloomberg tied yesterday to his overarching plan to improve the city’s environment and reduce its greenhouse gas emissions by 30%.

He also disclosed that the city would soon start offering property tax abatements to private building owners who install solar panels to generate electricity. And he said the city would issue a request for proposals this fall to find a private company to install solar panels on a number of city buildings.

In addition to his solar power proposals, the mayor pledged that by July 2008, 30% of the heating oil that the city purchases for municipal buildings will contain 5% biodiesel, a fuel made from renewable sources such as vegetable oils.

Also yesterday, Mr. Bloomberg traveled to Roosevelt Island to announce that two businesses there, a Gristede’s Supermarket and a parking garage, are getting their electricity exclusively from underwater turbines. “If the project is successful, the East River could become home to more than 300 turbines, producing an annual amount of energy equivalent to 68,000 barrels of oil,” he said.

In Union Square, Mr. Bloomberg walked through the green market with Messrs. Nelson and Mellencamp, stopping to snack on snap peas.

Mr. Nelson, who cracked a joke about marijuana that drew laughter from the mayor and the rest of the crowd, said Farm Aid makes sense in New York because “more people eat probably around here than anywhere in the world.”

Tickets for the September 9 benefit concert — which will feature Messrs. Nelson and Mellencamp, along with Dave Matthews and Neil Young — go on sale Saturday.