When Congressional candidates raise money during their campaigns, as they all must, the potential threats to political integrity are evident. Those threats become greater but less visible when candidates rely on bank loans to be repaid after the election. It's one thing for candidates to collect money prospectively, in anticipation of positions they will take and votes they will cast. It's quite another for senators and congressmen, once in office, to have to stagger along under debts to be paid off with money raised, week by week and vote by vote, during the session. For most people in Congress, fund-raising has become a continual preoccupation. But fund-raising to pay the debts of past elections is particularly onerous and places a legislator under unusual pressures.

The election financing laws and the banking regulations take note of the unwholesome possibilities here. But it's not easy to write tight rules. Fairness itself sometimes justifies heavy borrowing. The law does not limit the amount of his own money that a candidate may spend. For a person running against a rich opponent, personal borrowing -- which, like personal spending, is exempt from any limit -- may be the only way to conduct a comparable campaign. A congressional candidate's individual supporters are prohibited from contributing more that $1,000 each, and beyond that, in the heat of the campaign, the only hope often is a quick trip to the bank.

As this practice becomes more common, a further danger emerges. The banks can become the contributors of last resort. The federal regulators tell the banks that loans to political candidates must be made only on normal commercial terms. There are to be no below-market interest rates, and there are to be fixed dates of repayment. The bank examiners require banks to make the same efforts to collect political loans that they would apply to other loans. But repayment after the election is frequently difficult. There is always the possibility that the defaulted loan becomes a disguised political contribution by the bank -- which, like other corporations, is forbidden to contribute.

In campaign financing, public disclosure is the best and only real protection of voters who want to know what obligations the candidates are incurring. Voters need to keep in mind that bank loans are not neutral. Substantial debt mounting during a campaign is a warning signal. It means that the candidate, if successful, will remain under unusual financial pressure while in office. It also means that the lending banks will at least expect, as the phrase goes, to have their phone calls returned.