Attorneys for murder suspect Wayne B. Williams today continued their two-pronged defense, trying to portray him as a serious young man who wanted to help poor black children and attacking the testimony of prosecution witnesses who placed Williams with two of his alleged victims.

Among 13 witnesses called by the defense today were three black teen-agers who met Williams in the course of his efforts to form a singing group called "Gemini."

Three teen-agers and their mothers testified that Williams had never expresed distain for poor blacks and that he never made homosexual advances or "improper suggestions" to them.

Several prosecution witnesses have testified that Williams used racial slurs in talking about blacks from low-income areas. Two witnesses have said that Williams made homosexual advances to them and a third said he saw Williams holding hands with Nathaniel Cater, one of the two men he is charged with killing.

Broderick Burns, now a high school senior, testified today that he went to Los Angeles with Williams several years ago so that Williams could play a cassette recording for a producer he knew. "I think he wanted to let the guy know how I sounded," Burns said.

Williams apparently fell victim to a winter cold or an intestinal virus today. He complained of nausea this morning and, at the direction of Superior Court Judge Clarence Cooper, was taken from the court at noon to the detention center of a county hospital where he was examined by a physician.

After Williams hurriedly left the courtroom at 3:30 p.m., Cooper ended the day's proceedings. The trial will resume Tuesday.

Carla Bailey, who said she has known Williams for five years, today contradicted the testimony of Kent Hindsman, an aspiring songwriter who said he once rode in a car with Williams and 15-year-old Joseph (Jo-Jo) Bell. Bell is one of 10 young blacks whose deaths prosecutors contend fit a pattern with the two young men, Cater and Jimmy Ray Payne, whom Williams is accused of murdering.

Bailey said she remembered riding in Williams' station wagon with Hindsman and a young black singer named David Stephens. Hindsman has testified that the singer was Bell.

Bailey said Williams knew a teen-ager named Joseph Bell, but said it was not the same Joseph Bell whose bloated body was found in a river on April 19, 1981.

Bailey also said Hindsman was mistaken when he testified that during one recording audition she passed him a note apparently written by Williams that read, "I could be a president, I could be a mayor, or I could even be a killer."

She said the note was from one of the boys who had written an autobiography as part of his audition, and that it never mentioned the word "killer." But under cross-examination, prosecutors brought out several inconsistencies between Bailey's testimony today and written statements she signed for police investigators last summer.