WASHINGTON — Three decades ago, a middle-aged doctor sat outside his northern Michigan home and saw a patch of endangered paradise.

A beekeeper and amateur naturalist of prodigious energy, John Tanton had spent two decades planting trees, cleaning creeks and suing developers, but population growth put ever more pressure on the land. Though fertility rates had fallen, he saw a new threat emerging: soaring rates of immigration.

Time and again, Dr. Tanton urged liberal colleagues in groups like Planned Parenthood and the Sierra Club to seek immigration restraints, only to meet blank looks and awkward silences.

“I finally concluded that if anything was going to happen, I would have to do it myself,” he said.

Improbably, he did. From the resort town of Petoskey, Mich., Dr. Tanton helped start all three major national groups fighting to reduce immigration, legal and illegal, and molded one of the most powerful grass-roots forces in politics. The immigration-control movement surged to new influence in last fall’s elections and now holds near veto power over efforts to legalize any of the 11 million illegal immigrants in the United States.