Supreme Performances . . . For Comeback-of-the-Month, April's winner is William Crisp, Raleigh attorney for the Utilities Commission of North Carolina. Crisp, arguing a case before the Supreme Court on April 21, slipped and called Justice William H. Rehnquist "senator."

"Justice," Rehnquist corrected.

"Justice Rehnquist," Crisp said. "I would apologize, but I'm afraid there may be a senator in here and that might get me into trouble."

The line brought down the house.

For Groaner-of-the-Month, April's winner is also William Crisp. Later in his argument, Crisp, looking in Justice Sandra Day O'Connor's direction, said of his client's actions: "It's like that old adage about the lovely lady: You can look, but don't touch. And we didn't touch. We looked, but we didn't touch."

Personnelities . . . A new hire at the Office of Personnel Management may presage the birth of Washington's next Power Couple: she is the wife of OMB Director James C. Miller III.

Demaris Miller, a research psychologist now doing graduate work at George Washington University, was recently hired as a part-time GS-11 to perform what her boss at OPM calls "hard number work," validating data for 24 hours a week. Constance Horner, head of OPM, said that Miller was very careful not to apply for the job through political channels, and instead went anonymously through the procedures that any job-seeking graduate student would follow. In fact, one OPM source said that Miller seemed "overqualified" for the work she began doing this week.

Flat Earth Society . . . Don't let anyone tell you the Census Bureau has no sense of humor.

One of its regular chores is to track the "population center" of the United States -- estimated for 1985 to be a spot in west-central Washington County, Mo. Its definition of the population center, census officials say, is the point where "the country would balance perfectly if it were a flat surface and every person on it had equal weight."

By this measure, the nation's population center is in fact a sparsely populated area close to the Mark Twain National Forest, 10 miles northwest of Potosi, Mo.

Since the 1980 census, the population center has moved more than 20 miles west and almost 10 miles south from its 1980 location near DeSota, Mo., in Jefferson County, confirming a southwest drift. The westward trend has been fairly steady since the early 1970s, the bureau said, while the southward trend has lessened since 1980.

But stand by: the bureau says it won't identify the exact center until the 1990 census.

Batting Average . . . A historical footnote: Wednesday's Supreme Court ruling banning racial discrimination in jury selection was a milestone of sorts for federal judge Constance Baker Motley.

Motley, who in 1966 became the first black woman appointed to the federal bench, argued 10 cases before the Supreme Court during her career with the NAACP Legal Defense and Educational Fund, Inc.

Her last case -- and the only one she lost -- was Swain v. Alabama, the ruling the justices overturned on Wednesday, finally agreeing with Motley's arguments.

Motley, now chief judge of the U.S. District Court for the Southern District of New York, was elated by the ruling. "It's certainly a great feeling to be kind of vindicated after 22 years," she said.