NEW YORK (Reuters) - Goldman Sachs Group (>> Goldman Sachs Group Inc) on Wednesday attacked expert evidence offered by attorneys for former female employees in a U.S. federal sex discrimination lawsuit, arguing there was no pattern of gender-based pay and promotion disparities at the bank.

In the first day of arguments in a case launched in 2010, a lawyer for two former Goldman employees said the Wall Street giant displayed a "consistent" pattern of sexual bias, while the bank's attorney said such accusations were "baseless."

Cristina Chen-Oster, a former vice president at the firm, and Shanna Orlich, a former associate, together have accused Goldman of fostering a "boys' club" atmosphere where work-related events were held at strip clubs.

The women are seeking class certification and monetary damages for claims that Goldman consistently under-paid women executives and gave them lower performance-review marks.

"The pattern is consistent and clear," said plaintiffs' attorney Kelly Dermody at the court hearing in the Southern District of New York in downtown Manhattan.

She cited a statistical analysis done by Henry Farber, a Princeton University economics professor, which found that female vice presidents at Goldman on average earned salaries 21 percent below their male counterparts, while women associates earned 8 percent less. Farber's research, commissioned by the plaintiffs, also claimed to show gender discrimination in evaluations and promotions.

Goldman Sachs' attorney Robert Giuffra took issue with Farber's findings and called the accusations "baseless" and "unfair." He told Magistrate Judge James Francis the numbers presented by the plaintiffs "reflect a really flawed, overly simplistic model."

Goldman contends Farber and the plaintiffs are conflating the company's investment bank, investment management and securities divisions, even though each unit has many sub-divisions with widely different responsibilities and salaries.

The bank cited its own expert, Michael Ward from Welch Consulting in California, who found no consistent pattern of disparities based on gender when the different units were taken into account.

"They are throwing mud at Goldman Sachs and it's wrong," Giuffra said. If the judge grants class certification in this case it would be "unprecedented" and lead to thousands of separate trials to determine damages because each job description and pay grade is so individualized, he said.

In addition to protests about pay, the former employees claimed the bank fomented an exclusionary culture where 75 women filed formal complaints of sexual harassment and reported seven incidents of rape or sexual assault, Dermody said in court.

Chen-Oster alleged in the original complaint that she was marginalized at the firm after reporting an incident in which she faced unwanted and aggressive sexual advances from a male colleague following a night of drinking at a topless bar.

The company then promoted the male employee, while Chen-Oster's career stagnated, according to the complaint.

Goldman Sachs denied the allegations in the suit and Giuffra said there was no evidence for the strip club claims.

Other sex discrimination cases, mostly brought in the late 1990s, have resulted in multi-million dollar settlements from banks such as Citigroup (>> Citigroup Inc), Merrill Lynch and Morgan Stanley (>> Morgan Stanley) for violations of Title VII of the 1964 Civil Rights Act.

The case is Chen-Oster v. Goldman Sachs & Co. in the U.S. District Court, Southern District of New York, No. 10-cv-06950.

(Reporting by Mica Rosenberg; Editing by Kevin Drawbaugh and Alan Crosby)

By Mica Rosenberg

Stocks treated in this article : Citigroup Inc, Goldman Sachs Group Inc, Morgan Stanley