Are the race riots in Margaret Thatcher's Britain a portent of what is going to happen here under Ronald Reagan? Certainly they carry far more meaning for our immediate future than the racial troubles that shook this country in the mid-1960s. Even so, the British model provides only the poorest guide for the United States. And those, like Gov. Hugh Carey of New York, who assert that American cities are due for the fire this fall, show reckless irresponsibility.

The American race troubles of 1965 to 1968 found their distinguishing feature in a background of flush prosperity and confident, liberal government. Unemployment was around 4 percent, and inflation around 3 percent. Lyndon Johnson was in the White House, and the Great Society enjoyed its heyday. There was a particular emphasis on making good -- yesterday if possible -- the wrongs done to blacks in this country over the past two centuries.

The sparks that set off the flames -- especially between police and minority groups -- were generated by frictions always present in modern urban life. But the dry leaves ready for burning came from a mixture of high expectations and slow delivery of promised boons. That is why -- except beween cops and blacks -- there was so little violence between the races. That is also why the troubles subsided so quickly when Richard Nixon and the Republicans came to office with prescriptions for lowering expectations.

Mrs. Thatcher, in stark contrast to Lyndon Johnson, presides over a right-wing Tory government dedicated to discipline and the smack of authority. She derides as "wets" those within her own cabinet who seek to ease the bite of unemployment. She hangs tough, on legalistic grounds, against the self-starvation tactics used by the jailed terrorists of the Irish Republican Army.

Her economic policies, moreover, have combined with Britain's longstanding inability to compete in international markets to yield a marked deterioration in living conditions. Last year in Britain, inflation rose and output dropped. Unemployment hit 10 percent, the highest figure since the Great Depression. The rise in joblessness between May 1980 and May of this year was 70 percent -- a staggering increase.

Intense competition for low-level jobs is one result. It is not only black immigrants who are going into the streets against the police. In town after town, white toughs are also going into the streets. Moreover, the racial tensions brewed in these situations seem to be whipped up even further by harsh confrontation between the government and the left wing of the Labor Party opposition. Hence the unseemly rows in the House of Commons.

The Reagan administration shares many of the ideological frills of the Thatcher government. The president and other prominent figures like to talk tough about fighting inflation and riding herd on big government and wasteful spending. But there the similarity stops, and hugh differences assert themselves.

The American economy, unlike that in Britain, enjoys an underlying buoyancy. The pressure exerted on consumer demand for goods and services by the Reagan administration is relatively moderate. In many parts of the country -- notably the Sun Belt -- there are opportunities galore. Unemployment in the country at large rose in the past year by less than 10 percent. Thanks to a strong dollar, and to good breaks on energy and food, inflation seems to be tending down.

Many poor people, depending on transfer payments from the government, will undoubtedly suffer as a result of the cuts now being made in projected federal spending. But the bite will probably not be felt for many months. It is at least possible that the Reagan administration is right in claiming tax cuts will induce a new burst of economic activity by that time. Certainly there is scant prospect for the surge in unemployment that devastated Britain -- and particularly young people in Britain -- during the past year.

Nor is the political opposition in this country militantly left wing as it is in Britain. The Democrats are scrambling to outdo the Republicans in granting favors for business. Only a minority inside the Democratic Party battles all-out against cuts in social spending. Even the organizations professionally concerned to defend the interests of the chief victims of spending cuts -- the Urban League, for example, and the NAACP -- are moderate in tone.

So nothing writ large in social or economic conditions requires that the Untied States under the Reagan administration suffer the kind of racial strife that now tears Britain apart. If such trouble occurs here soon, self-conscious imitation will play a role, and those who now predict racial flare-ups are literally asking for trouble.