IF YOU'D LIKE to take a trip back to your own and your parents' and grandparents' past, head on down the Pennsylvania Turnpike to the rambling concrete block buildings housing the antiques flea markets of the Pennsylvania Dutch country.

Outside, the present in the form of strip highway shopping centers, tourist attractions and long streams of impatient drivers is overtaking the easy-going Amish in their horse-pulled buggies. Inside, the past still reigns.

The markets of Pennsylvania, as epitomized by Renninger No. 1 in Adamstown and Renninger No. 2 in Kutztown, are major repositories of all the things great-grandmother threw away or relegated to the attic. They're a browser's paradise. You can wander among their hundreds of booths for hours to the tune of a Sousa march played on a crank-model Victrola. As you roam the cluttered aisles, you almost expect to hear the voice of comedian Eddie Cantor singing a '20s tune coming from the old-fashioned arched wooden radios.

The past is all here in a glorious jumble. Old Life magazines, player-piano rolls, Depression glass, high-button shoes, top hats and bowlers, frilly '20s frocks, wooden farm tools, 1900s postcards, oak ice-boxes, brass beds, a hand-operated ice-cream maker, dainty dolls and battered metal toys, four-string banjos from the flapper era-all the artifacts of earlier generations.

What piques the interest is the unexpectedness, the helter-skelterness of the markets. An ornate brass chandelier hangs next to a homely bucket, an iceman's tongs next to cowbells. There are genuine antiques here as well as old furniture and memorabilia. The Saturday we visited Renninger's No. 2, we found Stiegel glass, a floral-decorated toleware coffeepot, a Shakerstyle rocker, an inlaid, circa-1840s chest, a signed set of painted Hitchcock chairs, a 200-year-old dovetailed cherry cradle with Pennsylvania Dutch-style heart motifs among the collectibles.

At Renninger's No. 2 just outside of Kutztown in the "Hex country," with 250 indoor dealers open Saturdays, and Renninger's No. 1 in Adamstown near the Amish country, with 372 indoor exhibitors open Sundays, you can browse away a whole weekend year-roung. In warmer months another hundred or more dealers exhibit outdoors. These two are the area's largest antiques flea markets and claim to be the country's largest. But there are several other smaller markets for the compulsive browser to explore in the Adamstown area. Down the road from Renninger's No. 1 is Black Angus, with 70 dealers, in a brand new building, and offering more good-looking furniture, less memorabilia and less clutter. And there's the (Fridays only) Green Dragon in Ephrata, the outdoor Schupp's Grove, (closed in winter), Hummerstown Market and others.

Part of the fun of these markets is talking to the dealers, who are as miscellaneous as their wares. Some are full-timers with antiques shops of their own in the area. Others are part-timers who do one-day market stints. They range from a bulky lumber jacket-clad dealer, with cigar, rasping voice and offhand take-it-or-leave-it attitude, to a friendly older couple, the Zimnys of Anne's Attic Antiques, who tell you selling is "only a hobby with us" and who enjoy telling you about their finds. They say they comb the countryside, follow the country auctions for their wares, and get customers from Texas, Nebraska, Illinois, Michigan, as well as from the Northeast. Their wares include a tea chest from the ship Philadelphia, a late 1800s Pennsylvania hearth bench, an early 19th-century desk and a set of four painted country chairs.

Other dealers like Scott Brodston, an amateur musician, are collectors whose selling augments their hobbies. His booth had a fine miscellany of musical antiques among other items.

He also had a stack of old sheet music at reasonable prices: 50 cents to $2 for specials such as the spectacular multi-color battle scenes by E. T. Paul which are collector's items. At another booth, E. T. Paul's sheet music went for $9 and up.

This is another bonus at these large markets. Prices vary and you can sometimes get a "buy" by looking further. And you can also bargain. Dealers seem amenable to dickering. The prices can range from under a dollar for knickknacks to hundreds of dollars for a corner cupboard or a cherry drop-leaf table.

It's possible to spend an entire weekend going from one market to another without catching a glimpse of the nearby lush Amish farms and the many points of interest nearby. All of the big markets offer food-everything from hot dogs to such regional specialties as funnel cake. At Renninger No. 2, which shares the building with a farmer's market, you can buy fresh produce in season and watch a yound couple making fresh peanut butter. This market is off by itself and an hour's ride away from the cluster of Sunday markets, including Renninger No. 1, around Adamstown. But you can go antiquing in the small shops along the way.

Renninger No. 1 benefits from being the queen bee market in a section with other tourist facilities-several motels and restaurants, and antiques shops, plus a well-stocked visitor's center with brochures on where to stay, eat, sight-see, and go antiquing in the Pennsylvania Dutch country.

Besides handy antiques-trail guides to the area, the center material directs you to museums that give a sense of the antiques characteristic of the Pennsylvania Dutch country. These include the Pennsylvania Farm Museum and a working Amish farm open to visitors. In both, typical antique furnishings can be seen-the sort of items that occasionally can be found in Pennsylvania's bounteous antiques flea markets. Even if you don't find them, the fun is in the hunt. CAPTION: Illustration, no caption; Picture, An Amish father and son. Christian Science Monitor photo