It's on the level! This is the week of the brick

In case you forgot to mark it on your calendar, this is National Brick Week - officially proclaimed by President Reagan ''to reemphasize to each citizen in the United States the importance of brick and the industry that produces it.''

Now that proclamation isn't intended to make you skip and hop on the way to breakfast this morning, but it is hoped that you will sit up and take a little more notice. So, consider this:

* The first colonists to come ashore in Virginia in 1607 were brick masons. Along with the ship's carpenters, they brought a vital skill to the New World. After all, who better than a brick mason to lay the foundations on which a great nation would subsequently be built?

* Many of the brick buildings those early masons put up are still around. They have stood the test of time - several centuries of it, in fact. Virtually all standing buildings of historic significance that predate the break with George III are of brick, as is most of Williamsburg, Va. Then there is Monticello, Mount Vernon, and Independence Hall, to name more sites of historic significance.

* Most Americans prefer brick siding, though not all would-be homeowners feel they can afford it. But despite the high initial cost of brick, it has some long-term paybacks. It doesn't need painting or staining; it doesn't rot, and is particularly unpalatable to termites. In several states, too, fire insurance costs are as much as 22 percent lower for brick homes.

* There is no shortage of brickmaking clay in these United States, except in Hawaii (of volcanic origin) and Florida which, as a gift of the sea, is one long , gigantic sand bar. In other words, the country is not likely to run out of bricks in a hurry - which is more than can be said for several other building materials.

Even before the first attempts at colonization here, England's energy needs and the demands of a great navy and trading fleet had stripped away its major forests of Robin Hood's day. So the brick masons stepped in, more than adequately, to meet housing and other construction needs. Now, in the US, some experts suggest a timber shortage lies ahead. But the brick masons assure us that they are more than ready to fill the breach.

It is a much-circulated myth that all of the early brick buildings in colonial America were built of the brick ballast brought over from Europe on the trading vessels of those days. But the records suggest otherwise. While brick ballast from the ships was used here, there was nowhere near enough to meet the building needs of the day. The vast majority of bricks were locally made.

In colonial times the term ''brick mason'' referred to more than a bricklaying builder of walls; it meant that the man was a brickmaker as well. Just as soon as those ship's carpenters began taking stock of the available timber here, the brick masons were seeking, and finding, suitable clay deposits.

George Washington supervised the manufacture of bricks on his estates both before and after he distanced himself from Britain. Part of Mount Vernon is built of homemade brick, and the first section of the United States Capitol was constructed of bricks made right there on the Capitol grounds.

There was a time when hundreds of family-owned brickmaking plants dotted the landscape. There were 60 such facilities on the banks of the Hudson River alone, just north of New York City. Today the national total is down to 172, ranging in size from small, $10 million-a-year operations to the biggest - Acme Brick of Fort Worth, Texas - which turns out 900 million bricks a year. The nationwide total is 9 billion bricks a year.

Currently brick siding accounts for 30 percent of the US housing market, but the country's 300,000 bricklayers are hoping that an interested public will boost that figure in the years ahead.