When U.S. Ambassador to Mexico John Gavin resigned abruptly on April 8, he spoke of wanting to "return to the private sector and explore new challenges." According to sources close to Gavin, the challenge he has settled on is an "important position" with Atlantic-Richfield Oil Co.

A spokesman for Arco first said he didn't know whether it was true that Gavin had accepted a job there and that he would "have to check with management"; he called back and said "it's policy at Arco not to discuss any personnel matter, and beyond that I can't comment."

Asked if the Los Angeles-based company does business with Mexico, the spokesman said, "Yes, we do buy crude oil from Mexico. But we're basically a domestic company. A very, very small proportion of our oil is imported."

In any case, Gavin's experience in Mexico would be a mixed blessing for a new employer -- he has been much criticized by the government and the news media there for his frequently outspoken criticism of Mexico.

Gavin's resignation takes effect May 15. An embassy spokesman in Mexico City said he knew nothing specific about Gavin's future plans and that Gavin was in California to accept an honorary degree and deliver a commencement address at Pepperdine University in Malibu.

Put to the Test . . .

As she promised last month, Sen. Paula Hawkins (R-Fla.) has put her staff to the test -- the urinalysis she advocates for all federal employes. About 60 staffers, some in Washington and some in Florida district offices, submitted to a testthat identifies the presence of cocaine, marijuana or opiates.

One female aide reportedly quit rather than take the test.

The ground rules for the others, who will know their results next week, are that any staffer who tests positive can undergo a more detailed test. If evidence of drug use is found by the second test, the staffer will have a choice between entering a drug-treatment program or finding another job.

Hawkins has promised that she, her husband and her three children will also take the test.