Federal regulators are preparing a handful of lawsuits against former directors of failed savings and loan associations. Several will involve charges of alleged criminal fraud, said Thomas P. Vartanian, general counsel of the Federal Home Loan Bank Board.

Savings and loans have lost billions of dollars in the past two years, and more than 500 of them have been merged out of existence. Although the industry's difficulties are overwhelmingly the result of high interest rates driving down the yield on mortgage portfolios, some suits will charge that a few executives were responsible for, or profited from, their institutions' demise, Vartanian indicated.

Vartanian would not disclose which institutions are under investigation.

The suits are intended to demonstrate that, just because the industry is in financial trouble, the officers and directors do not have "a license to engage in abusive actions using public deposits entrusted to regulated institutions," according to Vartanian.

He said the first of four cases his staff is investigating would be filed in approximately three months. The Bank Board intends to concentrate on the less than 10 percent of those mergers where financial assistance was provided by the Federal Savings and Loan Insurance Corp. Vartanian added that the investigations were likely to continue, given the growing number of mergers.

Right now his staff is working on cases of S&Ls merged last year. Vartanian said the investigators are focussing on "sweetheart loans" to individuals on favorable terms, speculation in financial futures, excessive legal fees, and lucrative severance agreements to institution officials, commonly called "golden parachutes" or "golden handshakes." He noted that one S&L paid its lawyers $500,000 in the final week before it died.

The most serious offenses -- those where criminal fraud charges are likely to be brought -- involve unauthorized transactions in which the officers of mutual S&Ls profited from their mergers into other mutuals, he said. (Unlike stock companies, mutuals belong to the depositors.) Vartanian said such a case might involve a side agreement in which an officer sells his rights in property or a service corporation to the acquiring S&L at a beneficial price.

Apart from the current investigations, the bank board is involved in civil litigation with two failed S&Ls, Fidelity Savings and Loan of San Francisco and Unity Savings and Loan Association of Chicago.

Unity, owned by Bass Financial Corp., lost $23 million and its net worth fell to $2 million during the last nine months of 1981 before it was merged in late February of this year with Talman Home Federal Savings and Loan Association of Chicago. Unity was one of three failing Chicago thrifts absorbed by Talman at a cost to the FSLIC of $10 million.

Before the merger was consummated, Unity Chairman Saul Bass, his sons Howard and Mitchell, and three other executives obtained large severance contracts -- "golden parachutes." On March 3 the FSLIC sued the five officers for allegedly trying to arrange a secret cash payment to themselves if the S&L failed. The next day a federal judge granted a preliminary injunction halting the payment of $334,000 to these executives, who had been fired by Talman the day before. The FSLIC is trying to get the judge to rule the severance payments invalid and return the escrowed money to the receiver.

Bass Financial Corp. responded by suing the government to get the federally engineered merger into Talman rescinded. Bass' suit charges the FSLIC with not giving adequate notice before placing Unity in receivership. The FSLIC has asked the court to dismiss the suit.

Fidelity Savings and Loan Association, a subsidiary of Fidelity Financial Corp. of Oakland, suffered an operating loss of $56.9 million in 1981.

Although it has assets of $2.9 billion, its net worth had sunk to just $20 million. Unable to borrow more from the Federal Home Loan Bank of San Francisco, Fidelity was declared insolvent and seized by the FSLIC on April 14.

After much controversy, Fidelity was acquired by Citicorp in August at a cost of $165 million to the FSLIC over a 12-year period.

A severance agreement would have provided Fidelity President A. C. Meyer Jr. with $226,300, and other officers with a total of more than $200,000 if they were fired after a regulatory merger. Meyer owned 20 percent of Fidelity's stock; his ex-wife, another 20 percent; and its attorney, 13 percent.

Meyer made loan commitments to builders at fixed rates when business was booming. But when interest rates failed to decline in 1979, Meyer had to provide loans at below-market rates. To cover commitments, he borrowed $1.4 billion from the Federal Home Loan Bank.

When the Federal Home Loan Bank told Meyer he would be placed in a special loan program designed to discipline poorly managed S&Ls, he retaliated by suing the bank, alleging that it charged Fidelity more than other banks.

Meyer also sued the federal bank in an attempt to recover $62 million in penalties and excess interest he alleges that it levied against Fidelity.

In addition, he sued the bank board and the FSLIC for an allegedly illegal takeover of Fidelity. He won in federal court, but the decision was reversed on appeal. Fidelity has moved for reconsideration.

If it loses, the case will revert to the lower court, where the judge will determine whether Fidelity's financial condition was indeed unsound, requiring that it be placed in receivership.

The suit against the Federal Home Loan Bank of San Francisco has been held up at the request of the FSLIC pending the outcome of the receivership case. Should the first case be decided in favor of the FSLIC, the second case would be moot.