* Two shareholder derivative complaints filed

* Accused of breach of fiduciary duty

(Adds Goldman declining to comment, details on SEC watchdog)

NEW YORK, April 23 (Reuters) - Goldman Sachs Group Inc GS.N Chief Executive Lloyd Blankfein and other bank officials have been sued by shareholders in two lawsuits related to fraud allegations brought by the federal government.

In complaints filed in New York State Supreme Court in Manhattan, Robert Rosinek and Morton Spiegel accused Goldman executives and the bank’s entire board of breaching fiduciary duties by letting the bank enter transactions involving risky collateralized debt obligations tied to subprime mortgages.

They said the defendants had “engaged in a systematic failure to exercise oversight” over the transactions, known as Abacus, and did not properly vet how the deals were structured and marketed. The plaintiffs also said the officials had failed to ensure Goldman did not represent “conflicting interests.”

The lapses had subjected Goldman to “billions of dollars” of liability and serious damage to its reputation, they said.

The lawsuits are derivative lawsuits, which shareholders bring on behalf of companies to enforce or defend rights that the companies fail to address on their own.

Goldman spokesman Ed Canaday declined to comment. Lawyers for both plaintiffs did not return calls for comment. The complaints were filed on Thursday and docketed on Friday.

Legal experts expect Goldman to face more litigation, including class-action complaints, after the U.S. Securities and Exchange Commission filed a civil fraud lawsuit on April 16 against the bank and Fabrice Tourre, whom the regulator called a key architect of Abacus.

The SEC said Goldman had failed to tell clients that securities they were buying were created by hedge fund investor John Paulson, who stood to benefit if the securities lost value.

Paulson made about $1 billion on Abacus, roughly the amount other investors are believed to have lost.

Late on Friday, the SEC Inspector General David Kotz, the regulator’s watchdog, said he would examine what factors drove the SEC to file its lawsuit.

Some Republican lawmakers have implied political moves were behind the decision and the timing. The lawsuit was announced days before the Senate was set to begin formal debate on financial reform legislation. [ID:nN23232748]

Goldman shares fell 12.8 percent on the day the SEC filed its lawsuit. The company has called the SEC allegations unfounded. Paulson has not been charged.

DERIVATIVE COMPLAINTS

In the derivative complaints, Rosinek and Spiegel characterized Goldman directors as “antagonistic” to their lawsuits, making it “futile” to approach them.

Thomas Dubbs, a senior partner at Labaton Sucharow LLP in New York, who specializes in class action cases, declined to comment on the Goldman litigation, but said derivative actions can face an uphill battle when shareholders do not go to the board first before suing.

“Investors might argue that it would be an empty gesture to ask a corporation to sue its own officers and directors,” he said. But “courts almost always require that hurdle to be jumped,” he added.

The lawsuits seek declarations that the Goldman defendants violated their fiduciary duties, plus compensatory damages. Goldman itself is a “nominal” defendant. Companies sometimes accept governance changes in resolving derivative lawsuits.

The law firm Faruqi & Faruqi LLP in New York represents both plaintiffs. Spiegel is also represented by Gardy & Notis LLP of Englewood Cliffs, New Jersey.

The cases are Rosinek v. Blankfein et al, New York State Supreme Court, New York County, No. 650318/2010, and Spiegel v. Blankfein et al in the same court, No. 650319/2010. (Reporting by Grant McCool and Jonathan Stempel; additional reporting by Steve Eder; editing by Ted Kerr and Andre Grenon)