Until a few weeks ago, the activities of professional pressure groups had been one of the few deep, dark secrets of American political life. With an understandable reluctance to expose dirty legislative linen to the public eye, Senators and Representatives have kept closemouthed about the techniques of lobbys. The lobbyists themselves were not talking; and the art and science of influencing lawmakers was a well-closeted skeleton.

Then, while the controversial natural gas bill was under heated debate on the floor of the Senate, South Dakota Senator Francis Case revealed that an oil company's agent had contributed $2,500 to his campaign fund in the hope that Case would respond with quid pro quo.

The legislators, with remarkable alacrity, appointed a special committee, headed by Georgia's Walter George, to investigate the Case incident. This move, however, did not completely satisfy the lawmakers; they decided to establish another committee to make a broad inquiry, covering the entire scope of lobbying activity.

After two weeks of bickering over the latter committee's personnel, the new investigation seems almost ready to begin. Headed by Arkansas' John L. McClellan, the special body will undertake a comprehensive inquiry which, if it can dig out the full story on lobbying, should prove most salutary both for the Senate and for the nation. But beyond its educational function, the McClellan group can serve a useful purpose by recommending much-needed changes in federal laws regulating lobbying.

The existing law undertakes to regulate two distinct types of pressure group activity. First is approaching Congress members in Washington, which comes under the purview of the Regulation of Lobbying Act of 1946. This law requires the registration of "legislative representatives" and the publicizing of their expenses and backers. While this Act has not worked perfectly, it probably cannot be changed for the better. Congress is unable to abolish the lobby because the First Amendment guarantees interest groups the right to petition legislators.

The second form of lobby technique, through campaign expenditures in the constituencies, should receive careful Congressional consideration. Federal laws regulating campaign expenditures are notoriously inadequate. Through large contributions, placed in strategic constituencies, lobbies can exert great influence on lawmakers without ever going to the Capitol.

Present federal laws limit the maximum campaign funds which any individual can spend on behalf of any candidate. The law also restricts the total amount which can be spent on any campaign. But these regulations can easily be circumvented and have been in many instances. They do not, for example, place the burden of responsibility for campaign expenditures on any particular person. The regulation on the candidate's spending does not prevent the prospective Senator from shoveling excess funds to his State Committee or to a special group to be used on his behalf.

As a consequence, fantastic amounts are often spent for the election of Senators and Representatives. One expert estimates that, in populous states, over $5 million may be required to elect a Senator. Federal law condones expenditures of one-tenth this size. The task of finding campaign funds often places the newly-elected Senator at the service of some interest group that has supported him, whether or not he obtained the money in payment for future services.

This form of lobbying should be met by new laws and a general tightening of present restrictions. The new regulations could be made more realistic by raising the limit on campaign expenses and making the candidate directly responsible for money spent on his behalf. Failure to observe the law should constitute grounds for expulsion from Congress. A revised law should also make it a misdemeanor to contribute to a campaign fund without informing the candidate and receiving his written acceptance of the contribution.

If enacted, these changes in federal campaign expenditure laws would prevent the recurrence of incidents like the Case affair. With the prestige of the McClellan committee behind them, these revisions might pass before the next election. The McClellan group should, therefore, recommend the changes and Congress should enact them.