IS THERE A DECLINE in the Gross Political Product -- the amount of money raised for and spent on American political campaigns? Many people think that would be a good thing; they're fed up with 15-second political spots and candidates who seem to campaign the calendar around. But the fact is that money is needed for the effective advocacy of political ideas and causes. What is important is the kind of money raised and by whom.

The news for 1985 is that the two parties raised less at the national level than they used to. The Democratic National Committee, for example, raised $7 million last year -- far less than its $22 million in campaign year 1984 or $11 million in 1983. The Republican congressional campaign committee raised $19 million in 1985, compared with $32 million in 1984 and more than $26 million in 1983. The Republicans' national, senatorial and congressional committees raised a total of $93 million last year -- well behind the pace that enabled them to raise $245 million in the 1983-84 cycle. The Democrats are even farther behind. Their three major committees raised less than $16 million in 1985, well behind the pace they need to match their $65 million in 1983-84 and, of course, far, far behind their Republican counterparts.Put these results together with the fact that total spending on Senate campaigns in 1983-84 was down slightly from the two previous years, and you have a startling contrast with what has previously been a sharp upward trend in political money dating at least to the beginning of effective federal disclosure laws in 1971. But not all money is cut off. Members of Congress, especially members of the tax-writing committees, have been raising money at record rates this year. They may spend it at similar rates next year -- or hold onto it if it succeeds in scaring off effective opposition.

There is good news and bad news here. Good news, in that hysterical and exaggerated direct mail appeals seem to be bringing in less money. The bad news is that the parties have been weakened and special economic interests have become more important to politicians. In 1981-85 the two parties achieved unusual cohesion on many issues, partly because of the political strength of the parties. Now the prospect is for more fragmentation. No one has a good answer to the question of how to arrest these trends. But it is a question Congress should give some attention to when it gets down to revising the campaign finance laws.