It's as if the nation had swallowed a solvent and were breaking up into our constituent parts - or, to be chemically more consistent about it, coming unglued. I can't remember a time in Washington when interest group issues and politics so dominated events. And every day the units of protest and concern seem to be subdividing into even smaller and more specialized groupings - these miners, those farmers, certain public employees, some gas producers and so forth. What's going on? Why has the nation's capital taken on the aspect of a glorified state legislature?

To be fair about it, it's not only the federal government that is feeling the pressure. Even as I write, I note that Toledo schoolteachers have gone out on strike, and a significant number of Washington-area doctors, displeased with their group-health arrangements, are threatening to do the same. It's a nation-wide pattern. But rarely has a president's time and attention been so consumed by the economic demands of particular groups. Consider Washington's agenda and some of its most hostly contested issues: Social Security taxes and payments, civil service salaries and perquisites, military pensions, tax credits for parents of private-school students, farm prices and income, steel prices, coal wages . . . the list goes on.

A labor lobbyist I know was observing the othe day how this atomizing of constituencies was apparent in his own attempt to get some manpower legislation passed. He didn't try to arrange meetings of his "coalition" any more, he said, but rather just dealt one-on-one with the various elements involved: mayors, unions, welfare organizations and the rest. That was because these days each was only inclined to "go in and try to save its own piece of the program."

President Carter clearly had something similar in mind when, in his speech on inflation, he spoke ruefully of a widespread "preoccupation with self," deplored the attenuated sense national purpose and community it reflected and concluded: "We favor sacrifice, so long as someone else goes first. We want to abolish tax loopholes, unless it's our loohole. We denounce special interests, except for our own." Hard-hitting, eloquent stuff - but the trouble is this: No one believes that presidential exhortations will be enough even to oslow the process, let alone to reverse it. And plenty of people think that Carter himself has inadvertently contributed to the trends in the country toward ever greater assertiveness of ever smaller interest groups.

I stress the word "trend" because poor Jimmy Carter, being blamed for floods, droughts and most of the pestilence stalking the land today, can hardly be said to have brought all this to office with him - although I do believe that in some ways, which we will get to in a moment, he has made it materially worse. But one must begin with the trends, and first among these is the much-remarked-upon popular loss of confidence in the nation's leaders and institutions.

This does not just mean, as the more romantic among us would have it, that people are concerned about the rectitude of their government. Surely, it also means that they have lost confidence in government's ability to deal effectively with the economy - with inflation and unemployment. And this being so, groups are rushing to get "theirs" while there is time. It's almost as if we had developed - all of us - a looter's mentality in the presence of the shattered storefronts of so many administrations' economic policies. The Carter administration has not exactly reversed the trend or covered itself with glory in this connection.

There is also the cumulative impact of what has been called "interest-group liberism" and its legislative product. By now, there can hardly be a cultural, racial, regional, economic or professional group for whom the lawnmakers of Washington have not fashioned some special statutory blessing - a prerogrative, a grant, an examption, a reimbursement . . . something. It puts a premium on identifying yourself with the special subgroup and helps to thin, if not destroy, whatever feeling of larger national loyalty various citizens may have.

So has the well-documented decline of both major political parties, as well as the decline of labor unions. These were all, at one time, much stronger forces for the nationalizing of people's ambitions and interests than they are now. And no comparable national influence has taken their place. On the contrary, if anything they have been increasingly displaced by computerized, single-issue-oriented lobbying efforts - efforts complete with glossy brochure; stupendous direct-mail, grass-roots outpouring; and highly sophisticated, pinpoint pressures on the relevant members of Congress.

It needs to be added that the recent reforms of congressional practice and procedure and the revised rules governing campaign financing have accentuated this trend. There is far less partywide discipline or sentiment in Congress they days. The individual legislator is less accountable to or dependent on the hierarchy of his national party on the Hill, so there is less incentive to take a national-party view. Legislators are more preoccupied with state and district "casework," as they call it - and more vulnerable to interest'group heat.

Finally, there is the absence of war or any comparably vivid national danger to unite people. To be sure, anyone old enough to recall when "rollback" was an emotional rallying cry to push the Soviets out of Eastern Europe rather than a call to consider a hike in Social Security taxes will have no trouble deciding which is the preferable condition. Still, as Carter himself concedes - the business about the energy crisis being the "moral equivalent of war" was a doomed sense of common purpose and urgency that tends to go with high-risk business, to view its economic and energy imperatives in this light.

I think Carter has accelerated the opposite process by an overwillingness to settle claims and demands group by group and to yeild to various constituency pressures. And although the troubles didn't start woth him, he represents pretty much the only mechanism that can be used to deal with them now. For it is an ironic fact of contemporary life that even as people around the country, Jimmy Carter included, have beeen expressing great unease with the scope and reach of federal government, that government does have the distinctive capacity to draw people into a coherent national effort. Carter, notably and brilliantly, got the completing groups together in his campaign. But he still has not stopped dealing with them one by one and fogging over their conflicts and differences. The success of his anti-inflation effort is a thin prospect at best, but it will depend on his willingness and ability to alter this habit. And so, as a result, will the success of his presidency.