New York ? A year after the financial system nearly collapsed, the nation’s biggest banks are bigger and regaining their appetite for risk.

Goldman Sachs, JPMorgan Chase and others — which have received tens of billions of dollars in federal aid — are once more betting big on bonds, commodities and exotic financial products, trading that nearly stopped during the financial crisis.

That Wall Street is making money again in essentially the same ways that thrust the banking system into chaos last fall is reason for concern on several levels, financial analysts and government officials say.

• There have been no significant changes to the federal rules governing their behavior. Proposals that have been made to better monitor the financial system and to police the products banks sell to consumers have been held up by lobbyists, lawmakers and turf-protecting regulators.

• Through mergers and the failure of Lehman Brothers, the mammoth banks whose near-collapse prompted government rescues have gotten even bigger, increasing the risk they pose to the financial system. And they still make bets that, in the aggregate, are worth far more than the capital they have on hand to cover against potential losses.

• The government’s response to last year’s meltdown was to spend whatever it takes to protect the financial system from collapse — a precedent that could encourage even greater risk-taking from the private sector.

Lawrence Summers, director of the White House National Economic Council, says an overhaul of financial regulations is needed as soon as possible to keep the financial system safe over the long haul.

“You cannot rely on the scars of past crises to ensure against practices that will lead to future crises,” Summers says.

No one is predicting another meltdown from risky trading in the near term. Rather, the concern is what happens over time as banks’ confidence grows and the memory of the financial crisis of 2008 fades.

Will they pile on bets to the point that a new asset bubble forms and — as happened with mortgage-backed securities — its undoing endangers banks and the broader economy?

“We’re seeing the same kind of behavior from the banks, and that could lead to some huge and scary parallels,” says Simon Johnson, former chief economist with the International Monetary Fund.

Quest for profits

Some risk-taking is good. When banks are willing to invest in companies or lend to home-buyers, that nurtures economic growth by generating employment and consumer spending, feeding a cycle of expansion.

The problem is when banks’ quest for profits leads them to take on too much risk. In the case of the housing bubble, which burst last year, banks lent too freely to consumers with weak credit and wagered too much on complex financial instruments tied to mortgages. As real-estate prices turned south, so did the financial industry’s health.

Because the largest banks’ trading divisions make their bets with each other, their fortunes are intertwined. The collapse of one can threaten another — and another — if it is unable to pay off its debts.

This so-called counterparty risk is a major reason the Obama administration’s regulatory overhaul plan calls for the creation of a “systemic risk regulator.”

The administration is also seeking tougher capital requirements for banks, arguing that banks’ buying of exotic financial products without keeping enough cash on reserve was a key cause of the crisis. Treasury Secretary Timothy Geithner has urged the Group of 20 nations — which meets this month in Pittsburgh — to agree on new capital levels by the end of 2010 and put them in place two years later. Geithner hasn’t said how much extra capital banks should be required to keep on hand.

Need for revenue

Data from the April-June quarter show that the banks are leaning heavily again on their trading desks for revenue.

• During the fourth quarter of 2008, when the financial crisis made even the shrewdest bankers risk-averse, Goldman’s trading of risky assets nearly stopped. But in the second quarter of 2009, trading revenue had climbed to nearly 50 percent of total revenue, closer to where it was two years ago before the recession began. JP Morgan’s reliance on trading revenue has exhibited a similar pattern.

• Also in the second quarter, the five biggest banks’ average potential losses from a single day of trading topped $1 billion, up 76 percent from two years ago, according to regulatory filings.

The government hasn’t just watched banks resume their freewheeling ways and prosper. It has been an enabler in the process. The Federal Reserve, the Treasury Department and the Federal Deposit Insurance Corp. — during both the Bush and Obama administrations — have made trillions of dollars available to the biggest banks through bailouts, low-cost loans and loss guarantees designed to stabilize the financial system.