A generic liberal candidate for governor on the Working Families Party line would halve an Andrew Cuomo victory over Republican Rob Astorino, a Siena College released Tuesday found.

The poll shows that Cuomo, a Democrat running for a second term, would handily defeat Astorino, the Westchester County Executive, by 30 percentage points, 58 percent to 28 percent.

But should a liberal candidate running on the union-backed WFP line run as well, Cuomo’s margin of victory falls to 15 percentage points.

The poll found that under that scenario, Cuomo would garner only 39 percent of the vote, with Astorino and the WFP candidate each earning 24 percent.

Nevertheless, the poll found Cuomo still is well liked among self-identified liberals, with 70 percent holding a favorable impression him. Among Democratic voters, Cuomo’s favorable rating is at 69 percent.

Astorino, meanwhile, remains largely unknown to most voters, with 66 percent saying they had no opinion of him.

Still, a WFP challenger could pose more than just an existential threat to Cuomo’s re-election campaign, with liberals, New York City residents and black voters choosing an unnamed liberal candidate over him and Astorino.

Cuomo has come under criticism from groups and advocates on the left primarily for his stance on fiscal issues. The $138 billion budget approved last month included a package of tax cuts aimed at business and property owners.

At the same time, advocacy groups in favor of the public financing of political campaigns were angered by a budget agreement that created small-dollar matching program that was limited to the state comptroller’s race.

Cuomo’s has lined up closer with the base of the Democratic Party mainly when it comes to social issues such as same-sex marriage and gun control.

But with the rise of liberal Democrats like New York City Mayor Bill de Blasio, some left-leaning advocates have been increasingly restive with Cuomo’s moderate stances on taxes, spending and as well as his approach to public-sector labor.

Because of those concerns, the Working Families Party has not ruled out giving its ballot line to another candidate for governor this year — an unprecedented move for the party.

“While Cuomo continues to hold a dominant position in a head-to-head matchup against Astorino, his lead is cut in half when a WFP candidate perceived to be more liberal or progressive than Cuomo is added to the mix,” said Siena College pollster Steven Greenberg. “More than 30 percent of Democrats, liberals, union households, New York City and black voters opt for a liberal WFP candidate. In a three-way race, independents are virtually evenly divided with 31 percent supporting Cuomo, 29 percent the WFP candidate and 27 percent Astorino.

Overall, Cuomo’s favorable rating dipped slightly: from 58 percent to 34 percent last month to 57 percent favorable, 38 percent unfavorable this month.

His job performance rating remains unchanged, with 45 percent saying Cuomo is doing a good or excellent job as governor.

Meanwhile, few voters — 30 percent — say they have followed any news about the governor’s soon-to-be-disbanded anti-corruption commission, which is wrapping up its work after Cuomo and legislative leaders agreed to a package of measures overhauling the state’s ethics laws.

Forty-one percent believe corruption in Albany remains a “serious” issues, with 43 percent saying its somewhat serious.

Despite most voters not being aware of the Moreland Commission’s disbanding, most believe the measures approved to deal with ethics and corruption is not a good compromise, 53 percent to 28 percent.

“While most voters did not follow the news about the Moreland Commission and the budget compromise that led to its disbanding, the vast majority of voters think that corruption in state government is a serious problem. A strong majority – including 66 percent who heard at least some about the disbanding of the Commission – feel that the budget resolution was a bad compromise that didn’t do enough to end corruption,” Greenberg said.

In news that is sure to buoy the Independent Democratic Conference, the Siena poll found 58 percent of voters want to see a coalition of GOP and Democratic lawmakers continue to control the state Senate, including 64 percent of independents polled.

The Senate coalition continues to give Republicans most of the trappings of power they had when they had a clean majority in the chamber; they are now in a numerical minority.

Only 16 percent of voters want to see the Senate GOP in a clear majority, the poll found.

The poll was conducted between April 12 and 17 and surveyed 772 registered voters. It has a margin of error of 3.5 percentage points.

SNY0414 Crosstabs by Nick Reisman