If President Reagan does not seek a second term, the Republican Party faces a divisive split between moderate and conservative wings for the 1984 presidential nomination, Transportation Secretary Drew Lewis said yesterday.

"I hope he runs for a specific reason," Lewis told reporters at a luncheon. "I'd like to see us not have a split in the Republican Party."

Lewis, who is leaving the Cabinet Feb. 1 for the cable television industry, said he expects Reagan to seek another term.

"If the president runs again, I don't see either a serious split or a serious challenge" from the Democrats, Lewis said.

Considered one of the Cabinet's most politically astute members, Lewis said the vacuum created if Reagan does not run would probably result in "a candidate from the right and a candidate from the middle."

Lewis said he is reluctant to mention names, but suggested that a contest between Vice President Bush and Rep. Jack Kemp (R-N.Y.) might develop.

Lewis, who told Reagan in a private meeting last summer that the economy was in dismal condition, said he has noticed signs of an upturn that could bode well for Reagan in 1984. But if the economy continues to "founder," if the unemployment rate does not drop below 10 percent, if deficits in the $200 billion range persist, "we're not going to have a Republican president," he said.