What a nifty picture. What a positive message.

There, in the very office of the very Democratic speaker of the House, stood the very Republican president-elect. To all the world, he looked to be genuinely enjoying both himself and the company.

That's the kind of week it has been for Ronald Reagan: good pictures and even better reviews. Sure, the incumbend president is not the toughest act to follow in front of the Washington audience. But still, the Reagan moves have been deft and the style winning.

The suddenly-grown-introspective Democrats represent no immediate political threat to the next administration. But there are other threats, most of them posed by the differing expectations, contradictory agendas and internal tensions within the Reagan "coalition." That collection, which among other things enabled Reagan to become the first nominee since Ike to carry both Massachusetts and Arizona, encompasses spirited groups that do not now extend diplomatic recognition to each other.

This is much more serious than Sun Belt versus Snow Belt. The differences are substantive as well as stylistic, and they do get emotional.

For example, open warfare now rages between the more traditional budget-cutters and the more adventuresome tax-cutters. Since before the time of Alf Landon, the balanced budget has been an article of dogma professed, if not practiced, by Republican leaders.

Ronald Reagan, the cagey right-hander, respects tradition. But he very much likes the Laffer Curve, which argues that tax cuts produce increases in revenues. Those who believe Laffer is the best medicine must have been encouraged to see the president-elect dining on Tuesday with Washington Mayor Marion Barry. Barry's administration, in an effort to raise revenues, recently raised the city's tax on gasoline, making gas in the District more expensive than gas in Maryland or Virginia, a move that turned out just as Laffer would have predicted: when the D.C. tax went up, the D.C. sales went down -- and so, of course, did the revenues.

Even more bitter than the economic differences are the significant philosophical cleavages between the libertarian Republicans and the "morality-codifier" Republicans. The former, who are the more senior if less activist in the GOP, are not simply referring to IRS or EPA or OSHA when they speak out against excessive government intervention in people's lives. They resent and resist being told what -- and what not -- to do.

Not so with the codifiers of morality in the coalition. Like the liberal activists whom they detest, these codifiers would be hard pressed to think of a single phase of public or private behavior for which there should not be an appropriate statute or even a constitutional amendment. Movies and television will be cleaned up, you can be sure. While the old liberal codifiers seemed to delight in telling junior high school faculties and parents who could go to which sports banquet, the coming codifiers will probably concentrate on gym showers and reading lists. A national Commissioner of Heavy Necking could be proposed.

Then there are in the Reagan camp those who support federal aid to New York City and the Chrysler Corporation and those who oppose it. Until sometime after Labor Day, the president-elect stood with the latter group. He moved to the side of the federal aid advocates and carried both New York and Michigan, if that means anything.

What almost certainly did mean something -- votes for Reagan and against Carter in the farm states -- was Carter's embargo on grain sales to the Soviet Union. Reagan also won support from American businessmen who seek Soviet or Chinese markets for their carbonated soft drinks or their computer software. Yet the Reagan transition team publicly praises the think tank report that urges that our international trade be governed by politics, not by economics. And what about those cheap foreign imports?

Franklin Roosevelt held together a coalition that included Harry Byrd Sr. and Walter Reuther, intimidating city machines and intense academic reformers. It was a difficult process and it took time, skill and attention. Reagan will probably have his own talents tested long before Memorial Day by one or more of the groups already mentioned. It could be some policy question -- maybe homosexual rights or shipping subsidies or whether the feds should meddle in the trucking industry. After all, when the president-elect left the spearker's office, he stopped in to pay one more courtesy call down the street -- at the Teamsters. An interesting coalition.