WHEN HE DIED suddenly while campaigning for the Senate last month, Rep. John Ashbrook had $52,000 in his campaign bank account. His opponent, incumbent Howard Metzenbaum, had $1,003,000. These numbers say a good deal about congressional campaigns: the system tends to favor incumbents. And campaigns cost much more than they used to.

People deplore the high cost of campaigns. But the fact is that many Americans are, at best, apathetic about politics, and candidates who want to reach them must spend lots of money, primarily on television, sometimes on radio or direct mail. In 1974, when the current campaign finance law was passed, a 30-second prime time TV ad in Baltimore cost $1,100; today it costs $3,000. First-class postage is up from 8 cents to 20 cents.

Any system of campaign finance should allow candidates to raise enough money to communicate with voters. At the same time, it should not require them to raise money in ways that unduly distort the workings of the political process. The current system, a vast improvement on its predecessors, does a reasonably good job of enabling candidates to raise sufficient money. But it does not go as far as it could to hold down the influence of narrow economic interests and their political action committees (PACs) and to strengthen the importance of individual contributors.

To judge from the reports filed at the Federal Elections Commission in April, incumbents of both parties had no trouble raising enough money. On March 31, incumbent senators had an average of $491,000 in the bank--almost as much as the $616,000 average that successful candidates spent in these same races in 1976. Republican challengers in Senate races will do all right, too; they will receive the maximum allowable contribution from the national party--$73,000 in the smallest states, more in larger states ($572,000 in Ohio). Democratic challengers are not so fortunate. It's not that the rules are tilted against them but that they failed to develop a large base of direct-mail contributors, as the Republicans did.

Some changes could be made. The current $1,000 limit on individual contributions, set in 1974, needs to be raised to compensate for the rise in campaign costs. And thought should be given to lowering the $5,000 ceiling on PAC contributions. PAC contributions are not so important in the 33 Senate races (they accounted for 16 percent of receipts in 1980). But they are influential in the less visible 435 House races, in which PACs--most of them concerned more about specific economic rather than broad ideological issues --provided one-third of the receipts for incumbents in 1980. They will provide more this year.

That makes even more salutary a reform we have supported in the past: limiting the total amount of PAC money any candidate can receive. At the moment there is no active movement to revise campaign finance laws. That the system is working relatively smoothly, however, should not obscure the need for change.