Over the past few years, there has been a growing trend among vacationers to seek out the wild life." They aren't bound for Las Vegas or the Place Pigalle. They're heading for nature preserves and bird sanctuaries.

According, to the National Audubon Society, last year more than a million families visited sanctuaries. The society - the largest and oldest environmental and conservation organization in the country - said this market an increase in attendance of more than 20 percent in the past two years. Most of the new visitors came from the larger urban areas, the society reported.

And why are more and more families suddenly going to the birds on their vacations?

Strange as it may seem, the manmade, plastic family-fantasy worlds such as Disneyland appear to be one of the reasons. "It's not only the bird watchers who are flocking to the sanctuaries," an Audubon spokesman said, "but folks who have gone the family entertainment complex route and had their curiosity piqued about the real thing.

"Now they want to see the birds, otters, alligators and other creatures in their natural habitat as well as take in some of the most spectacular undeveloped areas there are," he said.

Another reason for the popularity is the price. Families are finding that visiting a sanctuary isn't going to break their budget. Generally, admission for adults is $3, $1 for students, and free for children under 12.

If you're a budding birder, don't worry about being thrown into an unfamiliar environment. Many of the sanctuaries open to the public have nature education centers with exhibits and classes on wildfire conservation and the environment. Here's a list of the 10 most ivisted sanctuaries across the nation. CALIFORNIA

Richardson Bay Wildfire Sanctuary, 376 Greenwood Beach Rd., Tiburon 94920. Located at the head of San Francisco Bay, it has a waterfowl sanctuary and a nature education center on its 900 acres of shallow bay and 11 acres of mainland. CONNECTICUT

Audubon Center of Greenwich, 613 Riversville Rd., Greenwich 06830. More than 400 acres of woods, open fields, ponds, streams and marshlands. There's a nature education center and an adult ecology workshop in summer.

Sharon Audubon Center, Route 4, Sharon 06069. Over 500 acres of mixed forest, two large ponds, running streams, open fields and marshland. It has a nature education center. FLORIDA

Big Pine Key, Box 510, Big Pine Key 33043. Covering almost 750 acres, it has a wildfire refuge to protect the endangered Key deer.

Corkscrew Swamp Sanctuary, Box 1875, Route 2, Sanctuarry Rd., Naples 33940. Located southwest of Immokalee, it has a mile-long boardwalk that winds through the heart of the swamp allowing visitors to view the last remaining large stand of 700-year-old bald cypress trees, other exotic flora, and a wide variety of wildlife including one of the two major remaining rookeries of the wood stork, the only American member of the stork family. MINNESOTA

Northwoods Audubon Center, Route 1, Sandstone 55072. Operated as a nature education center, it is situated on 535 acres in the east central part of the state and contains diverse habitat typical of the area.

NEW YORK

Theodore Roosevelt Sanctuary, P.O. Box 5, Oyster Bay 11771. Located on Long Island near the home of the former president, there are 10 heavily wooded acres and a nature education center. OHIO

Aullwood Audubon Center, 1000 Aullwood Rd., Dayton 45414. Situated on 70 acres of hardwood forest,with meadows, a stream, bog and pond, there's also a nature education center. SOUTH CAROLINA

Francis Beidler Forest Sanctuary, P.O. Box 47, Dorchester 29437. Located northwest of Charleston. A solar-heated visitor center and 6,500-foot-long boardwalk are the highlights of this forest located in the Four Holes Swamp, which contains the largest known tract of virgin tupelo-bald cypress left in the world. WISCONSIN

Schlitz Audubon Center, 1111 East Brown Deer Rd., Milwaukee 53217. The 185-acre facility contains the largest area of undeveloped land on Lake Michigan in the Milwaukee region. There's also a nature education center.

The Audubon spokesman said that the right attire for touring the sanctuaries is field clothing, such as jeans and comfortable walking shoes. He also points out that camping or picnicking is not allowed at National Audubon sanctuaries, but if you check with the sanctuary warden, he'll be able to direct you to nearby areas.

You can get a free brochure describing all Audubon wildlife sanctuaries, their addresses and telephone numbers, by writing to Frances Breed, National Audubon Society, 950 Third Ave., New York 10022. Of the 63 sanctuaries listed 10 are not open to the public; advance arrangements are necessary at 35 others.

The Tacoma Audubon Society has just published a comprehensive guide listing people in hundreds of areas in the United States and throughout the world who are willing to give the travelling birdwatcher and nature enthusiast information about where to go and what to see in their areas. The 76-page booklet, "Operation Nature Guide World Wide 1978-79," costs $3.95. It's available from the Tacoma Audubon Society. 34915 4th Ave. South, Federal Way, Tacoma, Wash. 98003.