Many Americans believe that on an average day, the average congressman joins a lobbyist for what is, between them, a six-martini lunch in furtherance of some conspiracy against the average American. If the average American thinks legislators should lead lives of travail, asceticism and insecurity, the average American should rejoice about the kind of days that Howard Denis lives. Welcome to the world of the state legislator: one-Coke lunches, heavy on tuna fish.

His 1974 Chevrolet has gone 96,000 miles and acquired that many dents and scratches carrying him to and from Annapolis and around his surburban Washington district. The district contains 56,506 registered voters. Four years ago, he won by 211 votes out of 26,905 cast. Before his two-year campaign is over he will have knocked on about 30,000 doors. In his six years as a state senator he has been bitten by five dogs, threatened with a shotgun and had his literature thrown in his face.

Politicians know better than to aggravate wantonly the electorate, so they smile until their cheeks ache, especially during the cruelest month -- October. About now, a candidate feels that he or she is a toy in the hands of Fate--a fragile toy in the hands of an ill-behaved Fate that should be sent to its room without dinner. Denis' salary as senator ($18,500) is a lot less than the fees (he's a lawyer) he must pass up for the pleasure of campaigning.

He looks 42, which he is. He should look dreadful, but doesn't. You would, if you were a Republican running in a district liberally stocked with federal workers who were not generally Republicans even before the Reagan administration arrived with its "RIF" (reduction-in-force) program for slimming the government. There are just seven Republicans among Maryland's 47 senators. The ratio is even worse in the House of Delegates, where only 15 of the 141 delegates are Republicans.

Denis' campaign will spend about $20,000, most of it for mailings. Madeleine Will, who is what Boss Tweed would have been if he had really meant business, lobbies for the Maryland Association of Retarded Citizens and has held a fund-raiser for Denis, who has been helpful to her cause.

He distributes a four-page newspaper listing numerous achievements, such as his support for community placements for the retarded, and better street lights to combat crime at the University of Maryland. He stresses the common issues of state government: education, the struggle with the big city -- in this case, Baltimore -- over funds. He also stresses seniority. Such is the wear and tear of the legislator's life, if elected to a second term he will be among the top 10 senators in seniority.

Thomas Jefferson's tombstone lists his three proudest achievements: author of the Declaration of Independence and Virginia's statute for religious freedom, and father of the University of Virginia. Denis' tombstone can announce:

Here sleeps the author of the truck cover bill.

Maryland truckers are not required to cover cargoes such as gravel, to the detriment of Maryland windshields. The truckers have an argument (costs) and so does Denis (other costs, such as for windshields), and of such arguments the fabric of politics is woven.

Denis' chores are not contemptible for being of less than Jeffersonian grandeur. Whose chores are consistently grand? Anyway, this nation cannot do without the profession of state legislator, which is more than can be said of, say, the columnist's profession.

Maybe it is because of the proximity of his district to the nation's capital, but Denis gets questioned about the Middle East as well as about Maryland. Many people are, to put it politely, vague about what state legislators are. Thy are the infantry lieutenants of American government. Many more Americans are reverent about states' rights than are ready to join, that s or support, or even notice the infantry.

Between the policeman on the corner and the president on television, not much of government is tangible, concrete, even visible. But the quality of roads, schools, parks, prisons-- among other things--depends on state government, where the ratio of work required to prestige received is awfully high.

When night spreads its mantle over America, when the nation puts its feet up and loosens its belt a notch, the nation can take its ease, and can take many good things for granted, in part because thousands of persons like Denis are putting their blistered feet in hot solutions of Epsom salts. Morning comes early for democracy's foot soldiers.