AS A WELL-INFORMED American, you will probably be surprised to learn that the men who wrote the Constitution intended the size of the House of Representatives to increase as the U.S. population increased. In fact, James Madison wrote in Federalist No. 57 that the census had two purposes: to apportion the House (that is, to distribute members to states according to their populations) and to augment the number of representatives. That's the way it worked for 120 years. In 1790, there were 105 House members; by 1910, there were 435.

Then, in 1920, Congress abruptly changed course. It decided to freeze the size of the House. Know-nothing sentiment was running rampant, and many nativists thought that holding the number of House members steady would effectively deny representation to immigrants. They were wrong, of course, but the result of that 1920 decision is with us today. Each House member represents about 560,000 people, compared with 211,000 in 1910 and 39,000 in 1810.

Now after 80 years of stagnation, is it not time to increase the size of the House once more?

I became convinced that the House has to get bigger after reading an excellent and exhaustive new study of the apportionment process by a father-son team of political scientists: John Kromkowski, president of the National Center for Urban Ethnic Affairs at Catholic University, and Charles Kromkowski, Thomas Jefferson fellow at the University of Virginia. They've raised the idea at just the right time. Americans are becoming more alienated from government as government has grown bigger and more important to their lives.

Like it or not, members of Congress have come to play a critical ombudsman role over the years. They're the main point of contact between the citizen and the growing bureaucracy. They're the ones Americans turn to in order to get that delayed social security check or apply for that SBA loan or even get a street paved. It's a critical, though not very sexy, role, and it grows more difficult as the size of districts and the size of government expands.

What is the ideal size of a congressional district? Madison liked the idea of each member representing 30,000 to 40,000 people. In Great Britain, each member of the House of Commons represents 80,000; in West Germany, 118,000; in Japan, 239,000. By any standard, 560,000 constituents is too many.

But that number will look small in the decades ahead. In another 40 years, it will probably exceed 800,000. The Kromkowskis show the absurdity of freezing the size of Congress by pointing out that, based on current estimates of the effect of the reapportionment that will follow the 1990 Census, New York will have the same number of House members in 1992 as it had in 1870; Iowa will have the same as it had in 1850; and eight other states will have the same or fewer representatives in 1992 as they had in the 19th century. Obviously all of these states currently have populations far larger than they were, say, a hundred years ago.

There's an even more timely reason to increase the size of Congress: Sentiment is building in the country for bringing new blood to the institution. Both conservatives and liberals, believing that incumbents are invincible, have called for limiting congressional tenure (12 years is the popular limit). While I think that the power of incumbency is vastly overstated and that limiting tenure is a terrible, anti-democratic idea, the unhappiness that's motivating the movement cannot be ignored. And it's true that Congress needs new blood.

But throwing congressmen out arbitrarily after their time has expired is not the way to get that new legislative blood. A far more efficient and equitable method is simply to enlarge the institution. Adding House members would have salutary practical effects as well: It would reduce the number of committee assignments and reduce the heavy workload that many members have to carry, freeing them to do a little thinking instead of a lot of running around.

Politically, expansion is also a good idea. Republicans will like it because it gives them a chance to get elected without having to fight the power of incumbency. Democrats will like it because it goes part of the way toward solving a problem that will grow more serious in the years ahead: minority representation. Current population trends show blacks moving out of center-city areas and into the suburbs. As that happens, it will become more difficult to draw black-majority districts. Adding more districts nationwide will ameliorate the problem, at least for a while.

There are other advantages. A major objective of the apportionment process should be to reduce the number of seats that states lose. Before 1910, the system worked exceptionally well. From 1870 to 1890, the Kromkowskis point out, only four states lost a seat in the House; from 1890 to 1910, no state did. But, according to projections, the 1990 census will cause five states to lose at least two seats each and as many as nine states to lose one. One of the biggest losers is Montana, which will probably see its House delegation cut in half -- from two representatives to one. The last time Montana had a single House member was in 1900, when its population was 243,000, compared with 806,000 today.

My own proposal is to enlarge Congress by 40 seats (9.2 percent) for the 1992 elections, an increase that would roughly keep up with the 10-year rise in population. Then we should keep raising the number at 10-year intervals, roughly in parity with the population rise, until the House becomes unwieldy. My guess is that 600 should be the maximum. (The British House of Commons has 650 members; the French Chamber of Deputies, 577.) Such an "augmentation" would have a healthy effect on the democratic process in this country by bringing new faces to Congress, by bringing Congress closer to the people and by reducing the all-consuming importance of redistricting.

Above all, enlarging the House would be easy. It doesn't require a constitutional amendment. A simple statute will do. The Kromkowskis call their study "Why 435?" Why, indeed? It's a number that has outlived its usefulness.

James Glassman is editor of Roll Call, a twice-weekly newspaper that covers Congress.