MY LAST visit to Ann Arbor, Michigan, was 12 years ago. This year, I decided to visit my close friends, Romy and Necie Aquino, long-time residents of Ann Arbor.

Both Romy and Necie are alumni of the University of the Philippines College (then Institute) of Public Health.

Romy was captivated by the beauty and serenity of life in Ann Arbor when he was pursuing his doctoral studies in environmental health at the University of Michigan. Necie was then working at the University of Michigan Medical Center, and their children Paolo, Patricia Ann and Enrico were attending private schools in the area.

Today, Romy is laboratory manager at McNamee, Porter and Seeley Inc., a tetra tech company established in 1914. His office is a mere 15-minute drive from their well-appointed four-bedroom home, with a spacious lawn and backyard, in a beautiful and tranquil neighborhood along Fairhaven Court in Ann Arbor.

Necie works at Ann Arbor's water and sewerage treatment plant. She's still a whiz in the kitchen and is the perfect host, guaranteed to make a transient's visit free from boredom and full of fun and laughter.

The children are now pursuing careers of their own.

The couple scheduled their annual vacation leave to coincide with my one-week visit to Michigan in Oct. 9-16 via Continental Airlines.

During my masteral studies at the University of Michigan in 1983, I had not been aware of Michigan's magnificent fall, which had been described as the most visually dramatic season in the state.

According to tourist brochures and magazine and newspaper articles, the best time to view Michigan is from mid-September to early October in the Upper Peninsula, between late September and mid-October in the northern Lower Peninsula, from early to mid-October in mid-Michigan, and from mid- to late-October in the southern Lower Michigan.

The fall color display peaks in stages, beginning at the top of the state where cooler temperatures arrive first, and moving downward.

My curiosity was aroused as to what makes the leaves change color. Writeups on this phenomenon say that weather conditions in early September largely determine the dramatically visual fall color display.

If there are bright sunny days and cool nights, it is said, one can expect a good display.

Daylight length is also important. Shorter days cause leaves to stop producing chlorophyll so that the leaves lose their green color. Rain also enhances growing conditions. If there is adequate summer rainfall, tree leaves will be bigger and healthier when they assume autumn colors.

Continuous cloudy weather is not good as this inhibits sugar production, which is responsible for the brilliant redness of the leaves.

Michigan has 18 million acres of forests with about 150 different species of trees. Its autumn foliage includes a mixture of red, yellow, gold and orange hues.

The fall color season is said to account for about 30 percent ($2.1 billion) of Michigan's $8.5-billion tourism industry. This year alone, AAA Michigan estimates that about 2.8 million state residents will come to view the fall color display, arriving by car, train, boat and hot air balloons.

My hosts and I decided to spend more time at St. Ignace and Marquette.

We reached the entrance to Tahquamenon Falls State Park in Paradise in the late afternoon, and immediately alighted from the car and followed its hiking trail.

The $4 entrance fee helps in the park's maintenance by the Parks and Recreation Division of the Michigan Department of Natural Resources.

Tahquamenon Falls State Park covers close to 40,000 acres spanning over 13 miles, much of it undeveloped woodland without roads.

The Tahquamenon River is the park's centerpiece. The river rises from springs north of McMillan and drains a watershed of more than 820 square miles. The amber color of the water is not from rust but tannin leached from the cedar, spruce and hemlock in the swamps drained by the river.

The Lower Falls runs four miles downstream (in addition to the trail, one has to go down 90 steps to enjoy the breathtaking view).

The Upper Falls trail took longer to cover by foot. One has to take 110 steps to reach a vantage point aside from the trail. The Upper Falls is one of the largest waterfalls east of the Mississippi. It has a drop of nearly 50 feet and is more than 200 feet across. A maximum flow of more than 50,000 gallons of water per second has been recorded cascading over these falls.

The trail leading to the Upper Falls took longer to traverse but was awesome and magnificent nonetheless. In one portion of the trail, I was reminded of a passage from high school:

''Through this toilsome world, alas!/Once and only once I pass/If a kindness I may show,/If a good deed I may do,/Let me do it now./Let me not defer or neglect it,/For I shall not pass this way again.''

Later, I discovered that a couple had been staring at me with amusement, for I had recited this passage out loud.

Why the unusual name of Tahquamenon? The Parks brochure says this is the land of Longfellow's Hiawatha--''by the rushing Tahquamenon'' Hiawatha built his canoe.

The Ojibwa Indians were attracted by the abundant fish in its waters and the animals along its shores. They camped, farmed, fished and trapped along its banks. In the late 1800s, the lumber barons came and used the river to carry their logs to the mills. Lumberjacks, who harvested the tall timber, were among the first permanent white settlers.

In spring and summer, camping, hiking, fishing, canoeing, nature study and photography are popular activities. Winter offers opportunity for snowmobiling, cross-country skiing and snowshoeing with miles of marked trails.

The next day, we proceeded to Marquette, the home of Northern Michigan University (Wildcats). We continued to enjoy the visual feast of the fall-color display at Presque Isle Park, where we spotted some deer along the hiking trail.

At the Ellwood Mattson Lower Harbor Park, there was this beautiful quotation: ''To be gone is to be missed, but not to be forgotten.''

Not to be forgotten by me is the Superior Dome, the world's largest wooden dome.

This building, all of 5.1 acres under one roof, opened on Sept. 14, 1991. Its height is equal to a 14-story building. It has served as the site of Northern Michigan University football games and commencement exercises, car/boat/builder/food shows, conventions, high school track meets and football games.

It was also in Marquette that I first tasted baked pasties made either with steak, with or without rutabagas, or veggies (broccoli, cauliflower, onion, green pepper, potatoes, mushrooms, celery, carrots), cream cheese and cheddar cheese. It's a bigger version of our empanada.