FOR OVER 20 years the Teamsters pension fund has been investigated by one government agency or another. In the process, it has acquired a larger importance as a symbol of union racketeering and corruption and a prime example of the difficulties of preventing and rectifying pension fund mismanagement.

Last week Labor Secretary Ray Donovan appeared before the Senate permanent subcommittee on investigations to report the progress of his department's probe of the Teamsters' fund. The secretary supported legislation to stiffen penalties for labor corruption--measures also endorsed by AFL- CIO chief Lane Kirkland yesterday--and pledged vigorous pursuit of both civil and criminal allegations. Any effort to speed up resolution of the Teamster fund matter is certainly welcome. Miracles, however, should not be expected.

The issues involved in the continuing civil litigation --launched six years ago by the Labor Department under the new pension protection law passed by Congress--are enormously complex. Over one million pages of documents have already been gathered, and thousands more are being sought. The Teamsters' lawyers have taken full advantage of the many opportunities for delay built into the judicial process, and they will surely continue to do so. Responsibility for pursuing civil and criminal charges will still be split between the Labor and Justice departments, although the administration has elevated the status of their three-year- old joint task force and Secretary Donovan has promised to improve information-sharing between the two departments. Nonetheless it is likely that litigation will drag on for years in the pattern so familiar to prosecutors of antitrust and other complicated corporate cases.

The most urgent need is to make sure that the almost $3 billion now in the pension fund doesn't fall into untrustworthy hands. In 1977 the Labor Department and the IRS rescued the fund from its former trusteeship by muscling through a voluntary agreement under which new trustees were selected, and the fund was placed under independent control. That agreement will expire next year, and the present trustees have been reluctant to accept continuation of certain terms the government feels are essential for fund protection.

Resolving the Teamster pension matter is very important, but it will still leave open the larger question of pension protection. The Teamster case is the most prominent but certainly not the only case of possible abuse by corporate or union trustees. Policing every pension fund of any size would require an army of investigators and, even then, legal prohibitions would remain a weak deterrent because of the time it takes to secure a final judgment in the courts. The surest solution--certain to be mightily resisted by both companies and unions--would be to require independent management of all pension funds of any size.