If you were a tree, what kind of tree would you be?

All due respect to Barbara Walters, but none of the many celebrities that she has interviewed -- certainly not Ronald Reagan, who once argued that trees pollute, not even the arborescent Katharine Hepburn to whom she first posed the question a decade ago -- were better suited to answer it than are Andy and Katie Lipkis.

Never heard of them, you say? Probably neither has Barbara Walters. In any case, Andy Lipkis is kind of a modern Johnny Appleseed. He's not hung up on apple trees especially, though he likes them alright. It's just that he's terribly fond of trees in general. He's probably planted a thousand of them he'll admit to, maybe 5,000. With his own hands.

But he and his wife, Katie, don't like to boast about the number of the saplings they've planted, or the estimated million or 2 million trees whose plantings they inspired. They prefer to keep their vision trained on the forest rather than the trees.

"There's something emerging out there and it's really kind of wonderful," he says. "There's a strong passion for trees."

Andy Lipkis is totally serious about this. And, recently, the national audience and support for his Los Angeles-based group called TreePeople have blossomed as never before. Seventeen years ago, when the small-statured Californian, then a college freshman, first went out on a limb to undertake his own pithy brand of environmental activism by focusing on reforesting the earth, such talk of plants and passions was, at best, seen as just another alternative agenda. Something a bit wacko from the West Coast, perhaps, though benign enough in a Franciscan sort of way. At worst, his aggressive commitment to tree-dom was seen to be about as twisted as a baobob's branches.

But since Earth Day 1990, and in the past two years since the Greenhouse Effect gave the American public a meaningful image of planetary troubles ahead, trees are in. And so are Andy and Katie Lipkis, which is good news for their new book. "We're filling orders as fast as we can get the recycled paper," says a spokesman at Jeremy Tarcher Inc., publisher of "The Simple Act of Planting a Tree: Healing Your Neighborhood, Your City, and Your World" ($12.95).

"They are like the gurus of community tree planting," says Greg Elliott of Green ReLeaf, the urban tree-planting project of the Potomac Valley Green Network, part of the Green movement working locally for political, social, economic and ecological change. But Elliott, 30, a public policy analyst here, believes the couple is more accustomed to the shade of California sequoias than the spotlight of national attention. Recently, by coincidence, she was on the same flight from Philadelphia to Washington as the Lipkises, who were three days into a 17-city tour promoting their book. "I said, 'Aren't you Andy Lipkis?' He looked at me in shock and said no. Then he admitted he was."

Elliott, whose Green ReLeaf has twice planted trees in Anacostia, was there the next day when the Lipkises met with several groups committed to the regreening of this city's streets. "They conveyed the general sense of how to get community action going in the neighborhood," she says. "They really stress the self-reliance of community tree planting, that half of what you achieve is not just the planting of the trees, but the people coming together to accomplish something."

The Lipkises call it Citizen Forestry. "This movement is specifically people living in cities, getting out and planting trees around their streets rather than expecting their city government to do it," says Katie Lipkis, an Australian advertising copywriter who married the cause when she fell for Andy as he took his message Down Under in 1983.

"It's taking the streets back," interjects Andy Lipkis, who likes to mention the revolutionary nature of this scheme, even though both of them emphasize that citizen forestry is middle-of-the-road, down-home, apple-pie, mainstream American community action.

Although TreePeople has tackled such projects in past years as digging in thousands of saplings in the San Bernadino National Forest and replanting California mountain ranges, the Lipkises talk mostly these days about trees in cities, about "the urban forest."

"Our emphasis is cities because we think that's where most of the people are, and if we're going to enroll people in healing the environment, then we're going to have to do it where the people are," says Katie Lipkis. "And the fact is a city tree can work a lot harder on the environment in the city ... especially the inner cities. It's an area that most of the major environmental organizations have missed."

The environmental message, say the Lipkises, is that trees do good. Scientifically speaking, they help to clean air in smogged-up cities, cool heated-up urban temperatures and thereby conserve energy, invite back wildlife to concrete jungles, soften harsh urban landscapes, buffer noise. "Much of the push in citizen forestry is to give people permission and mobilize people to start directly attacking environmental problems," says Andy Lipkis.

But that's the simple part. Plant the tree and let it do environmental good deeds. The hard part, say the Lipkises, the part of citizen forestry that poses the greatest barriers and defeats the best of intentions, is maneuvering around city regulations that not only may deny people permission to plant a tree on public property, but might even cut down a tree planted without government approval. This is where the training workshops they conduct in California come in handy; this is why they wrote the book.

"There's sort of a contradiction in the title," says Katie Lipkis. "The act of planting a tree is simple like Zen is simple. It's not a complicated act, but it's a very complicated process leading up to it. If you find out you've got to get a permit from the city and it's going to take six months, then you're going to say forget it.

"We help people understand what the parameters are, what the landscape is, what the issues are that they need to appreciate. So if they are going to argue with city officials, they can do it grounded in a really good knowledge ... Groups that have worked with us have gotten their cities to outrageously bend their rules. So instead of setting them up for failure, we set them up for a stronger wind."

If the bureaucracy challenge turns the Lipkises hard-edged, they get a little sappy when it comes to the changes that occur in people who plant trees. They've seen the effect at a planting of 40 trees in hip Venice, Calif. They saw it along Martin Luther King Jr. Boulevard in Los Angeles last January, when 3,000 people "from all walks of life and all colors" showed up to plant both sides of a seven-mile stretch of inner-city street.

"The dream was to turn King Boulevard into a beautiful monument to Martin Luther King and the power he represented," says Andy Lipkis. "The community got so validated by seeing that people cared about them and that their own neighbors cared ... People really want to count. They're crying out to make a difference. But it's beyond theory when we are working with inner-city kids, some of them gang kids who really are seeking to make a mark, to validate themselves, to have a feeling of family.

"Planting a tree becomes an incredible expression of one's power. The ability to change a street in a day -- forever -- fulfills a lot of needs."

And if Andy Lipkis could be a tree? "I'd have to think a Redwood," he says finally. "It is the largest tree in the world. It produces one of the smallest seeds in the world. If it gets stepped on by an animal, it's all over. Yet it is the problems and the challenges and the setbacks that strengthen its bark, that make it stand up ... What's so important about that is that we are all like trees."

Digging In

For more information on urban tree planting:

Green ReLeaf planted its first tree in Anacostia two years ago and works toward "preserving the environment in ways that make sense," says Greg Elliott. For more information (202) 832-1108.

Trees for the City is a local project of the L'Enfant Trust, a 13-year-old nonprofit group that works to preserve historic easements on buildings and property. "We're seeking donations and trying to be financial contractor to put the trees in and collaborate with other nonprofit groups," says project director John Nelson. (202) 347-1814.

Global ReLeaf, a project of the American Forestry Association, encourages and educates people to plant trees. Call 1-900-420-4545, for an information packet, and part of the $5 telephone charge goes toward planting a sapling in a damaged forest site.