Rabbi, lobbyist and charity chieftain Shiya Ostreicher is one of New York’s most powerful political players — and now, thanks to state investigators, one of the most scrutinized.

He has a hand in five Brooklyn nonprofits that pull down millions of dollars in taxpayer cash and private donations. One is under state probe. Another’s murky paperwork has raised questions about its legitimacy. The president of that group says he didn’t know that he was on the board — let alone that he was its president.

In less than a decade, Ostreicher, 43, has outgrown his Orthodox Brooklyn base to become a force in city and state politics.

He is described as politically brilliant and on good terms with both Democratic Assembly Speaker Sheldon Silver and Republican Senate Majority Leader Dean Skelos.

“There’s nobody who has the access that he has, which is on both sides, and that makes him very, very influential,” said one insider closely involved in New York politics. “So when he wants to get things done, he can do it.”

He has also become a rainmaker for top politicians.

“If you need help with your business or your company or a project, you show up to him and you ask him for help, and then, in return, he then asks you to raise money,” the source said.

‘The Jewish District’

Among Ostreicher’s controversial accomplishments was helping enact a law that extends the state Tuition Assistance Program to rabbinical students — a benefit estimated at $18 million a year. Critics said taxpayers should not pay for religious schooling.

Assemblyman Dov Hikind praised the effort led by Ostreicher and his allies at Agudath Israel of America, a key Orthodox charity. Ostreicher has been registered as a lobbyist for the group since 2011, although he has worked with them for much longer.

“People told us it would be impossible to pass this legislation,” Hikind said in March 2011, when the measure passed, noting Ostreicher worked with him for 10 years to get it done.

Ostreicher also was among the leaders behind the creation of the state Senate’s “super Jewish district” in Brooklyn in Orthodox Midwood and Borough Park. The area had been split among six senators but lines were redrawn in 2012 to create the district with Skelos’ backing.

Simcha Felder, a Democrat and Ostreicher pal, won the seat in 2012.

Ostreicher belongs to the Belz Hasidic sect and lives in Borough Park with his wife and children.

“He’s an altruistic individual who cares deeply about the community,” said Ezra Friedlander, head of a Manhattan-based political p.r. firm that has worked with Agudath Israel.

Moreland investigation

But now Ostreicher’s activism is the subject of a high-profile state corruption investigation.

The Moreland Commission, in a report released this month, said it was investigating an unnamed storefront charity in the city that took in millions of dollars in state money but did not seem to provide many services. The Post identified it as Relief Resources in Borough Park, which has received nearly $3 million in state funds to offer mental-health services. Ostreicher is on its board.

The commission said it installed a camera outside the group’s office and recorded little traffic in or out. It also subpoenaed phone records that showed most calls to the group were short, “raising questions about how substantive the calls can actually be,” the report said.

Commission co-chair William Fitzpatrick confirmed last week that Relief Resources was under probe. Noting funds “certainly didn’t go to improve the health of anybody in New York City,” he asked, “Who got those dollars?”

The commission report notes the probe is in its early stages and has found no impropriety to date.

No Relief Resources principal would speak to The Post. The group said in a statement that it handled thousands of calls a month from people with mental-health issues. It said it has eight full- and five part-time staffers.

Sen. Martin Golden, a Republican whose district includes part of Borough Park, sponsored two grants for $250,000 each. His cosponsor was state Sen. Joseph Bruno, the upstate Republican majority leader who resigned in 2008. He was convicted of fraud in 2009, but it was overturned.

Sen. Malcolm Smith of Queens,, the former Democratic majority leader, sponsored a $300,000 grant to Relief Resources in 2009. Smith was indicted last year on bribery charges. His office had no comment on the funds.

Ostreicher has been on Relief Resources’ board since it opened in 2001. The group’s incorporation papers list his home address.

The group also got a $300,000 allocation from the City Council in the 2009 fiscal year. It was sponsored by Speaker Christine Quinn and Felder, then a councilman.

“They have an impeccable record of helping thousands of people with mental-health issues,” Felder told The Post. “Government is not doing enough to help this organization financially.”

Web of nonprofits

Ostreicher is also a board member of another group at the same address, Refuah Resources, which provides referrals for medical services. That organization received $91,000 in state funding from Hikind since 2006.

Ostreicher founded a third group, The Students Link, at his home in 2003. Its address and phone number are the same as Relief Resources.

The group says its mission is to help poor children, and in 2008 it funded renovations to upstate summer camps, filings show.

By 2010, it had started to “help defray the costs of weddings in the Jewish community.”

Last year, tax filings show, it took in $377,000 from “rental of a hall” and spent $400,000 on rent.

A spokesman for the group said it rents out the Tiferes Rivka hall in Borough Park and subleases the space to a caterer who provides low-cost weddings to more than 100 couples a year.

He would not provide a copy of the group’s IRS application for tax-exempt status.

Alexander Ornstein, listed as president of The Students Link in 2012, gave no further information.

“I’m not on the board of Students Link,” he told The Post. “Am I on the board of Students Link?”

He said he would respond to written questions but did not.

Ornstein and Ostreicher are on the board of yet another non-profit. In 2011, they applied to the state to open a health-care center at 620 Foster Ave. in Borough Park called Premium Health.

The patient base was to consist of those who used Relief and Refuah Resources’ services but didn’t have doctors. Almost all of the funding was to come from Medicaid, its application said.

The center opened this year.

Ostreicher also started a nonprofit company called Affordable Drugs in 2004. A woman who answered the phone there said it was a pharmacy that provided only fertility drugs. It’s located in the same Borough Park building as Hikind’s district office.

Affordable Drugs applied for IRS tax-exempt status in 2006 but apparently didn’t get it. The IRS has no record of the group.

Additional reporting by Carl Campanile