Lawyers in the legal battle over Ground Zero worker compensation could bag up to half of the billions available to pay 9/11 recovery workers for toxic injuries.

Defense firms hired by the city to fight some 10,000 claims have already raked in close to $200 million, and about $75 million has been spent on administrative expenses.

Lawyers for the workers -- who have yet to be paid -- stand to reap 30 percent to 40 percent of all settlements or judgments, based on their retainer agreements with World Trade Center responders.

How much money is up for grabs is the big question, now that the first trials for a dozen 9/11 workers are set to start May 16 in Manhattan federal court. The two sides are in secret, "intensive discussions" that Judge Alvin Hellerstein hopes will settle as many cases as possible.

At stake is a $1 billion taxpayer fund and as much as $3 billion in liability-insurance coverage, which includes the Port Authority's $600 million and policies held by WTC contractors.

The WTC Captive Insurance Co., a nonprofit governed by Mayor Bloomberg, has managed a $1 billion fund. The money was awarded by Congress to pay claims stemming from the Ground Zero cleanup.

The fund spent $275 million between 2004 and Dec. 31, 2009, on defense lawyers and administrative costs, records obtained by The Post show.

At the same time, the fund paid only a total of $320,000 to five workers with minor injuries.

Workers are livid.

"How do you justify earning $275 million without a settlement or trial?" asked ex-NYPD Detective John Walcott, who battled leukemia after working for months at Ground Zero and the Fresh Kills landfill, where debris was shipped and sifted.

The WTC insurance fund was down to $923 million on Dec. 31, largely burning through its investment earnings since 2004. Expenses drained $28 million in the last three months of 2009 alone, records show.

But the fund recently won a $200 million settlement with city insurance companies it had sued to help cover legal expenses. That takes the total available to about $1.1 billion -- although costs keep mounting.

Were that sum alone distributed today, it would mean an average of about $100,000 per worker, many of whom have suffered debilitating illnesses or died.

The lawyers say they'll go after untold billions in liability insurance held by the PA, which owned the Twin Towers, and by construction companies and the barge operator who transported rubble to Fresh Kills.

Hellerstein has ordered the insurance policies kept confidential.

Soaring stakes

Some 10,000 Ground Zero workers are suing for a pot of money that could reach $4 billion. Where the cash comes from and where it goes:

IN

■ $2B in private insurance policies

■ $1.1B in the city-run WTC Captive Insurance Co., funded by Congress to pay the claims of injured workers

■ $600M in Port Authority insurance

OUT

■ $275M in the Captive fund has already been spent on lawyers and expenses

■ 30-40% percent in fees will be taken off the top of settlements or judgments by the plaintiffs’ lawyers