The Labor Department filed a civil suit yesterday against Teamsters President Frank E. Fitzsimmons and other former trustees of the union's scandal-ridden Central States Pension Fund in hopes of recovering millions of dollars in allegedly imprudent loans.

The pension fund - principal source of retirement security for about 480,000 Midwest trucking employees - has been repeatedly tapped for "a series of questionable loan transactions," according to the lawsuit.

Some loans were made to individuals linked to organized crime and were used to bankroll gambling casinos, racetracks and risky real estate ventures, government sources said.

Other loans were made to ostensibly legitimate enterprises without any attempt to obtain appraisals of collateral, or were accompanied by unusual agreement to forgo interest payments or to defer payment of deliquent interest, according to the lawsuit.

The Labor Department lawsuit, filed in U.S. District Court in Chicago, did not include a specific dollar amount for which Fitzsimmons and 16 other defendants would be held liable.

Although fluctuating real estate values and a lack of information on the status of some of the investments has thwarted Labor Department attempts to fix potential losses, the current fund managers reportedly have estimated that potential losses could reach $500 million.

The complaint specified 15 cases in which the trustees "engaged in a pattern of violations" that reflected "imprudent behavior . . . [and] a failure to carry out their fiduciary obligations in managing the fund."

The suit lists multimillion-dollar loans that the trustees have made since 1975, many of them allegedly without adequate assurances that the money would be repaid. The suit also claims that when some of the borrowers went into default, the trustees made no effort to collect on the loans.

One such loan involved $25 million in pension funds haned over to the Stardust and Fremont hotels in Las Vegas, allegedly for improvements to the hotels.

The Labor Department said the trustees not only neglected to assure that the money was spent for hotel improvements, but also permitted the diversion of a "large sum" of the loan for other purposes. The other purposes were not specified.

Similar loans described in Senate testimony in July included $11 million payments to a Connecticut jai alai fronton, and race track loans in Florrida, Missouri and Pennsylvania.

Labor Secretary Ray Marshall conceded in a news conference that the government may encounter difficulty recovering the full amount.

"We hope to get it all, and we expect to get as much as we can . . . Obviously, if there are no assets, you can't expect to get blood cut of a turnip," Marshall said.

The lawsuit signaled the second phase of an extensive Labor Department investigation of the Central States fund begun in 1975 following reports of mismanagement and alleged links to organized crime.

The lawsuit is the largest government action brought under the 1974 federal pension law the Employee Retirement Income Security Act (ERISA).

The first phase of the Labor Department's action was the forced resignation last year of Fitzsimmons and three other trustees, which was followed by the turnover of control of the fund's assets to private, independent investment managers.

Subsequently, 12 more trustees quit the fund, all of whom were among the 17 named in the lawsuit filed yesterday. Nine union officials and eight trucking industry representatives were named.

Also named in the lawsuit were the fund's current administrator, Daniel J. Shannon, and Teamsters vice president Roy Williams, regarded as a possinle heir to Fitzsimmons. Another possible Fitzsimmons successor, Jackie Presser, was also named in the lawsuit.

Fitzsimmons responded last night that the lawsuit "should cause no concern for our membership covered under (the plan)." He said the plan is "fully solvent and more than able to meet its obligations through the 20th century."

Fitzsimmons said it was "regretable that the Central States Pension Plan had been singled out as a test case" by the Labor Department, while other private and public pension trusts are "either fully or partally underfunded and others are disarray."

The Central States fund, with a holdings book value $1.7 billion, is the nation's third largest private pension fund in terms of membership. It is the nation's 16th largest pension plan when ranked by size of assets.

Marshall said that although the lawsuit involves only civil charges under the new pension law, a Labor Department task force has turned over evidence to the Justice Department for possible criminal prosecution.

Marshall said his priorities remained "restitution first and prosecution second," adding that "the money will come from where we can get it."

Labor Department Solicitor Carin Clauss estimated that if the civil case goes to trial, it may take two years or more to reach final judgments. She acknowledged that while the trustees are personally liable for "imprudent" drains of the pensions funds, they could each file for bankruptcy and limit liability.

Marshall said the lawsuit does not mean the end of the Labor Department's investigation of the Teamsters fund, but he said that "patterns of illegal action" before the 1974 pension fund law took effect could not be pursuits.