The son of Judge Robert H. Bork said he is writing a book showing that judicial philosophy took a back seat to politics in the Senate defeat of his father's nomination to the Supreme Court.

"This is not a vendetta. This is an exercise in understanding the political process," said Robert H. Bork Jr., 32.

The younger Bork said he has taken a leave from his job as a business writer at U.S. News & World Report and accepted a fellowship at the Heritage Foundation.

He said he plans to complete the book by next summer, and is negotiating with several publishers. The book will not be published by Heritage, a conservative think tank employing about 40 full-time scholars, spokesman Herb Berkowitz said.

The Senate, in a 58-to-42 vote Oct. 23, turned down President Reagan's nomination of Bork to the Supreme Court. Bork, 60, is a judge on the U.S. Circuit Court of Appeals for the District of Columbia.

During the debate on Bork's nomination, he was portrayed alternately as a brilliant jurist and a dangerous extremist. Critics attacked what they called his narrow reading of constitutional protections and accused him of opposing the rights of minorities, women and consumers. Supporters complained that the confirmation process was distorted by an aggressive campaign by liberals.

The younger Bork said the idea for the book was born in the frustration over his father's defeat.

"I thought there was a story that needed to be told there, a story about the confirmation and a story of the judicial philosophy involved," he said. "This is not just pouring out my gut emotions."

The thesis of the book is that liberals and conservatives turned the confirmation into a battle because it involved what was perceived as the swing vote on the court, vacated by Justice Lewis F. Powell Jr., who retired.

"It was clearly a watershed battle in the history of the court," the younger Bork said. "I think that a lot of what my father stood for was lost."

The battle was not so much over Bork's philosophy, the son said, but about the political implications of an advocate of judicial restraint winning the swing seat.

The book will also deal with Judge Anthony M. Kennedy, the federal judge nominated to fill the vacant seat. Kennedy, although conservative, has not expressed such extreme views as Bork and is considered likely to win Senate confirmation.

The younger Bork said he thought of becoming an attorney, but never applied to law school and enjoys writing too much to quit journalism. "Sitting at the dinner table across from my father was not quite the same as going to law school. But I suppose I picked something up," he said.