KINGS PARK, N.Y. — It’s the dog days of August, and any prospect of a serious Democratic primary challenge has withered in the summer heat. But appointed Sen. Kirsten Gillibrand (D-N.Y.) is as dogged as ever, interrupting a three-day swing through western New York Thursday to travel to a peninsula on the north shore of Long Island. There, she greeted 3,600 senior citizens who were bused in from Brooklyn for a picnic sponsored by state Assemblyman Vito Lopez (D).

“It’s a very important event,— Gillibrand said, sitting at a rickety picnic table after 90 minutes of shaking hands. “Vito has been doing this for a number of years. I thought it would be a great way to introduce myself to all the seniors.—

By any measure, 3,600 is an impressive figure — and in New York, many senior citizens feel a duty to vote because they believe they will be struck down by the ghost of FDR if they do not. But the more relevant number for Gillibrand and all the office-seeking supplicants who trekked 40 miles east of New York City to Sunken Meadow State Park, is 1 million. That’s the number of registered Democrats who live in Brooklyn, and Lopez, who looks a little like the late actor Zero Mostel, just happens to be the Brooklyn Democratic boss — and one of the most important members of the Empire State Democratic establishment who hasn’t yet endorsed Gillibrand in the 2010 special Senate election.

“We’re nowhere near an endorsement at this point,— Lopez said unapologetically.

Not even, he was asked, when pressured by President Barack Obama and Sen. Charles Schumer (D-N.Y.), who have been busy clearing the Democratic field for Gillibrand?

“Not even for Domenic Recchia,— he replied, grinning mischievously and gesturing to a New York City councilman and loyal Lopez lieutenant who served as Gillibrand’s escort the entire time she was at the picnic.

Greeted deferentially by New York Mayor Michael Bloomberg (I) as well as by Bloomberg’s likely Democratic challenger, New York City Comptroller William Thompson Jr., and scores of other office holders and seekers, Lopez — who in one of those “only in New York— paradoxes is not, despite his surname, Hispanic — was clearly enjoying himself, sitting in a cordoned-off area in the middle of the picnic grounds.

One city council candidate shaking hands was a young man named Steven Levin, whose father is a first cousin to Sen. Carl Levin (D-Mich.) and Rep. Sander Levin (D-Mich.).

“Everybody comes here,— Lopez said. “Every candidate, every party. Somehow they find their way here.—

Lopez, who pushed hard for Caroline Kennedy to be appointed to the Senate when Hillary Rodham Clinton became secretary of State this January, couldn’t resist teasing Gillibrand about her increasingly strong political standing before sending her off to greet the hordes.

“You’re still a reformer — and that’s not bad,— he told her. “Everybody drops out.—Gillibrand, with Recchia and a handful of aides clutching campaign literature and point-and-shoot cameras, smiled uneasily before moving on.

For the next hour and a half, the earnest newcomer to the New York City political scene navigated her way through the bubbling ethnic cauldron of Brooklyn politics, moving through the food lines and picnic tables with Recchia enthusiastically introducing her. In stark contrast to Recchia, Gillibrand did not seem to sweat.

“She came all the way from Washington to say hello!— he said over and over again. Frequently, there was a glint of recognition, and when there wasn’t, Recchia added, “She took Hillary’s spot!—

Most people smiled politely and shook hands as Gillibrand offered greetings and posed for pictures. But a Filipino woman who met the Senator, Trinidada DiPaunjabog, jumped up and down and gave the thumbs-up sign with both hands, saying “all right!— and “great!— over and over again.

“I read the paper, I know who she is,— DiPaunjabog said.

At a table of Polish émigrés who live in the Brooklyn neighborhood of Greenpoint, one man complained that the weather was “too much hot,— but another, Michal Dzumjai, serenaded Gillibrand with stirring renditions of “God Bless America— and the Polish national anthem on his shiny red accordion. Everyone at the table stood and sang.

“I’ve spoken a little Spanish, I got to practice my Chinese, and I learned how to say thank you in Polish,— marveled Gillibrand, who lived for a time in China as a college student.

Because so many politicians were on hand, many were taking the measure of Gillibrand. Many noted that the former Upstate Congresswoman has been aggressive about trying to get to know the state and their communities. Thompson, the city comptroller who must battle the tens of millions of dollars that Bloomberg is going to spend to win a third term this November, said he’d be pleased to have Gillibrand — who told his daughter at the picnic that he’s running “a very important race— — campaign by his side.

“She’s got a slightly different point of view, but in the time she’s been in the Senate — you’re seeing someone working very hard,— Thompson said.

Lopez, while stopping short of an endorsement, was still trying to be helpful. As Gillibrand circled back to pay her respects again before taking off, he had a suggestion.

“You should stick around for a minute, there’s someone worth about 5,000 votes coming in,— he told her.

That someone was Rabbi David Niederman, a powerful Orthodox Jewish leader in the Williamsburg section of Brooklyn. Niederman offered Gillibrand a cordial greeting, but did not shake her hand, which is the custom under traditional Jewish law. He listened intently as she told him she plans to make her first official trip to Israel soon.

“It’ll be my first of many — it’ll be nice,— she said.

And later, as she was preparing to leave, Gillibrand said she was confident that she can eventually win Lopez over. Lopez used to be a full-time advocate for senior citizens causes before entering politics, and Gillibrand hopes to exploit the connection. A member of the special Senate Aging Committee, Gillibrand said she is working on the chairman, Sen. Herb Kohl (D-Wis.), to schedule a field hearing for the committee in Lopez’s district.

“We’re just getting to know each other,— she said of the Brooklyn power broker. “I think there’s going to be places where we can work together — on a local level and on a national level.—