Lewis du Pont Smith, the du Pont family heir who has joined the organization of political extremist Lyndon H. LaRouche Jr., testified calmly and articulately today as he sought to regain control over his life and his money.

Smith's family members, who previously have had Smith declared mentally incompetent by a Pennsylvania judge, presented a different portrait of the 28-year-old man who has lent a LaRouche group $212,000.

At a hearing in Chester County Orphans Court, the relatives said that Smith, who now lives in Leesburg, Va., where he works for a LaRouche-affiliated newspaper, shunned them after joining the LaRouche group. He crouched on his kitchen floor to avoid relatives who visited to drop off Christmas presents, one testified.

The relatives are seeking a court order placing a guardian in control over Smith. Such a guardian could remove him from the LaRouche group and arrange for psychiatric counseling. A decision is not expected in the case for about a month.

Smith -- dressed in a tan suit, sporting closely cropped hair -- coolly and without hesitation answered questions about his life in Northern Virginia.

"I believe that my family is capriciously and illegally and immorally trying to impose its will on me in regards to what I say and do," Smith testified. He said he believes his constitutional rights have been abridged by the incompetency finding. The finding means he cannot vote or marry his fiance, who was in the courtroom.

"Louis was responsive to all questions," his lawyer, James Crummett, said after the hearing. "I think some of his analysis of the du Ponts was not only articulate but insightful."

The hearing is the latest battle in a bitter 14-month war between Smith, on one side, and his parents, two brothers and a sister, on the other. Smith refused to shake the hand of his brother Hank when the two met in a court hallway today, but stared straight ahead.

In April 1985 the Smith family, of Paoli, Pa., persuaded Common Pleas Judge Lawrence E. Wood to bar Smith temporarily from transferring any more money to a LaRouche group after he'd lent it $212,000 in two months, all of it unsecured. About $190,000 has not been repaid.

Last November after testimony that Smith had a mental disorder, Wood ruled preliminarily that the University of Michigan graduate is incompetent, and is being exploited by "designing persons" in the LaRouche group. The judge named the Wilmington Trust Co. as guardian of his $1.5 million estate.

The November ruling means Smith can receive $5,000 a month of his money for personal use, but has little other access to it.

In Pennsylvania, such guardianship hearings are two-tiered, and today's hearing also dealt with Smith's objections to the earlier decision. Smith denies he is incompetent and says his family opposes him out of dislike for LaRouche.

Lawyers in the case said they know of few instances in which someone has lost control of his funds for giving money to an alleged cult.

Smith family members testified today they don't have his telephone number and have to leave messages for him elsewhere.

Smith's sister, Eleuthera Smith Grassi of Washington, said that last Christmas she and her mother visited Smith's Leesburg home unannounced to give him presents, and knocked on the door.

"I could see Lewis crouched behind the kitchen door on the floor," she said. Soon after, a LaRouche associate arrived in a car and asked them to leave. She said the associate carried messages between Smith and his relatives, and that, at one point, Smith said he would see them only if they would bring back his grandmother. She had died a short time earlier.

Smith's father, E. Newbold Smith, said family members went to court because they "felt we had a very sick son on our hands, getting sicker. It was a motive for rescue." Wood's earlier decision was based in part on Smith's statements in support of the apocalyptic message of LaRouche. In today's hearing, the family's attorney, Leonard Dubin, tried to show that the LaRouche group controls Smith's mind.

The judge, however, barred as irrelevant almost all testimony about Smith's ideology and associations with the group.

Under questioning from Dubin, Smith said he cannot think of any point on which he disagrees with LaRouche. Wood prevented further questions on Smith's feelings about what the judge called LaRouche's "bizarre" beliefs.

Crummett said declaring someone incompetent for political beliefs is "Orwellian." Crummett said only people who are "totally incapacitated" should be declared incompetent. He has filed a $500,000 counterclaim against the family charging harassment of Smith, as well as a request in federal court in Philadelphia for an injunction to stop the proceedings