IF YOU ARE traveling along Interstate 270 this summer, you might want to leave the highway for a few minutes and visit Frederick, Md. If you want to see what a really spick-and-span small city (population 30,000) looks like, this is the place.

When the Maryland Municipal League held a convention in Frederick two years ago, teasing delegates asked Mayor Ron Young how he had managed to get the citizens to wash down the streets for their benefit. But the mayor has no such persuasive power. None is needed. Frederick was originally settled by people who set great store by a shipshape city, and, rather magically, the tradition has been maintained.

To begin with, there is a citizen commitment to cleanliness and order which, repeated visits prove, is on evidence in every part of town. Sidewalks are swept, trash is securely bagged,and it is unusual to see even a piece of Kleenex or an ice cream wrapper on the street. The Boy Scouts volunteer for clean-up duty and the Downtown Merchants Association schedules regular days on which store owners and their employees lend a hand to spruce up. Looking over the results, a visitor feels like donning white gloves and running a finger along the curb.

These private efforts are more than matched by the city government. Working from the midnight shift, city workers collect the trash three times a week in every neighborhood. Downtown streets are swept six nights a week and every single street in the city is cleaned at least twice a week.

The National Trust for Historic Preservation has honored Frederick for restoration of the downtown area. More than 1,000 buildings have been renovated in the last five years. Six hundred new trees have been planted on the downtown streets, and plans have been drawn for the creation of a linear park that will run through the middle of the city.

Frederick is growing. It has attracted new industry and residents who commute to jobs in Washington and Baltimore. It is growing without losing that special sense of community pride which has made it a truly lovely city. The citizens and the government care about the physical appearance of the town. Their efforts dignify those who live there and dazzle those who drop in.