PAT ROBERTSON'S campaign has a problem -- and it may be a serious one. The problem is whether the sale of a computer by the campaign last month violated the federal campaign finance law. Back in January the Robertson campaign bought a computer system for $233,480 from a longtime Robertson associate. Most campaigns don't buy computers outright, but perhaps the Robertson campaign decided that its plans to raise large sums from direct mail made the purchase advisable. The Robertson campaign has in fact raised $11.7 million, much of it from direct mail, but it has also spent about the same amount, much of it to keep those solicitation letters coming. Direct mail can be a drain on cash (the Postal Service doesn't extend credit), and on Sept. 30 the Robertson campaign, evidently to raise cash, sold the computer system for $337,500.

This looks fishy, because computers usually go down rather than up in value, and because the purchase was made, according to Post reporter Charles Babcock, by "a shell company in Denver whose only identifiable official is a Robertson campaign aide." The Federal Election Commission has issued advisory opinions saying that campaigns shouldn't sell equipment for cash until they're over, and it is clearly illegal for a campaign to sell equipment above its market value to a supporter of the candidate. Such purchases are, practically and legally, campaign contributions, and the federal campaign finance law prohibits corporate contributions, and limits personal contributions to $1,000.

There could be an innocent explanation for these transactions. Perhaps, as Mr. Robertson's press spokesman suggested Thursday, the $337,500 sale included more equipment than was involved in the $233,480 purchase. Perhaps the shell company in Denver was actually owned by persons who dealt with the Robertson campaign at arm's length. Perhaps the prices represented reasonable approximations of the market value of this equipment at the times it was sold. But if the campaign purchased the computer system for a price under the market or sold it for a price over the market in transactions involving Robertson supporters, that would look very much like an illegal contribution of about $100,000.

This is not the only issue that's been raised about the financing of Mr. Robertson's efforts: the Internal Revenue Service is auditing the Christian Broadcasting Network, of which he used to be president, and the Freedom Council, which helped to involve Robertson backers in politics in Michigan, to see whether they've violated the law by using tax-exempt funds for political purposes. In the meantime, the Robertson campaign has yet to explain the computer system transactions. It should do so, and the Federal Election Commission -- aptly described in a recent article by Brooks Jackson of The Wall Street Journal as a "pussycat" rather than a "watchdog" -- should investigate to see whether the law has been violated.