Marlo Thomas said St. Jude had been in their lives so long that she and the other Thomas kids thought he was their uncle.

"Somebody said to me today, 'Do you pray to St. Jude, too?' I said no, I just tell Daddy and he does it. He has a direct line," the television star told an audience saluting comedian Danny Thomas last night.

The tribute climaxed a day in which President Reagan bestowed a Congressional Gold Medal on the 71-year-old entertainer for his "humanitarian efforts" in founding St. Jude Children's Research Hospital in Memphis, Tenn., 23 years ago.

"I was going to hug him," said Danny Thomas, "then I decided just to touch his face."

St. Jude, named for the patron saint of the hopeless, is one of 20 cancer centers receiving federal funds for research. Thomas said he didn't have to put in a plug for the hospital when he was with Reagan and Vice President Bush yesterday.

"They know what we're doing. They never cut us back. We get what we want," Thomas said of the $9 million that St. Jude receives in competitive grants. This year the research center's budget is expected to be more than $50 million.

Dr. Joseph Simone, St. Jude's director, told the dinner crowd of 300 at Knights of Columbus Hall in Arlington that when the hospital opened in 1962 no more than 1 percent of the children suffering from leukemia ever survived. Today, 50 percent of them live.

"The most exciting research area is that we're closing in on what the genetic reason is that cancer becomes cancer," Simone said before dinner.

Washington attorney Richard Shadyac came up with the idea of a congressional medal for Thomas. George Washington received the first such medal. Rep. Nick J. Rahall II (D-W.Va.) introduced legislation two years ago that made Thomas the 116th recipient.

The wheels of government grinding as they do, the White House notified Shadyac and others about 10 days ago that the presentation ceremony would be on the president's April 16 schedule. The combined efforts of something called ALSAC took over. By last night the ALSACers who stand for Aiding Leukemia Stricken American Children joined forces with the ALSACers who stand for American Lebanese Syrian Associated Charities.

In practice, if not in fact, they are one and the same. And they beamed paternally when their hero of the day stood before them to take their accolades.

"I knew when the president put [the medal] around my neck that he was putting it around the necks of everyone," Thomas said.