A 19-year-old San Antonio woman testified yesterday that Lon A. Lewis, who was charged with conspiracy to commit murder in connection with the Sept. 23 deaths of his wife and infant daughter in Bowie, told her in April that he was planning a surprise for her birthday, which was on Sept. 22.

Lewis, 28, was arrested along with Gene T. Meyer more than two weeks after Lewis' wife Carol and their 4-month old daughter. Heather, was found stabbed to death in the kitchen of their home at 4807 raemore La., Bowie.

Meyer was convicted of murder on April 27. Yesterday was the opening day of Lewis' trial in Prince George's County Circuit court.

Called as a prosecution witness, Kathy Nugent said that she had spent time with Lewis and Meyer, both employes of Data-Point Corp. a computer firm with its home base in San Antonio, when the two men were there for training sessions last year.

Earlier, during opening statements, defense lawyer Leslie Gladstone said he would try to prove that Lewis was charged after making an "involuntary statement" to police admitting that he and Meyer had agreed to a, "you-kill-my-wife, I'll-kill-yours" deal.

"The statement came after at least 10 polygraph tests and two days of questioning," Gladstone said following the morning session. "Unless the jury believes beyond a shadow of a doubt the statement was not involuntary they must find Lon not quilty."

Gladstone said he would not dispute the contention by police investigators that Lewis was having an affair with Nugent or that Meyer had discussed the plot with him.

"Lon never took what Meyer was saying seriously; to him it was all a fantasy," Gladstone said. "But Meyer was serious, he was a brutal man and he dominated Lon. He thought he could force Lon to kill his own wife by killing Lon's wife."

Meyer allegedly wanted to collect his wife's life insurance policy.

One neighbor, DuWayen Brown of 4808 Raemore La. testified yesterday that Lewis, "appeared to be in shock," when he came home from work that Friday evening and found his wife and daughter.

Gladstone said he definitely planned to put Lewis on the stand in his own defense. Both lawyers said they were expecting the trial to take at least until the end of the week if not longer.