Former Vice President Walter Mondale hasn't decided whether to run against Sen. Rudy Boschwitz in 1990, but Minnesotans give him a good chance of defeating the incumbent, a survey released Saturday shows.

The poll, conducted by the Minneapolis Star Tribune on Feb. 15-20, found 49 percent of the 701 Minnesota adults surveyed believed Mondale would defeat Boschwitz in a head-to-head race. Forty percent said they thought Boschwitz would win.Spokesmen for both men described the results as "interesting."

"It's too early for these numbers to be very meaningful," said Mondale's son, Ted, who has been urging his father to run.

Boschwitz's campaign director, Tom Mason, said the poll "confirms what everybody thinks. It would be a close, competitive race."

Mondale, who ran unsuccessfully for president in 1984, has said repeatedly that he does not intend to run for office again. He now works as a lawyer in Minneapolis.

Mondale has led Boschwitz in every published poll in the last 18 months.

An August 1987 poll of 757 Minnesota adults showed Mondale leading Boschwitz by 15 percentage points.

The latest poll, for which no margin of error was cited, showed a slight erosion in Boschwitz's job-approval rating. Those who "approve strongly" of his performance fell to 22 percent, the lowest since mid-1985. But his overall approval rating, which includes strong and weak approval, held fairly steady at 62 percent; he has never been below 60 percent during his second term.

The percentage who said they had no opinion about Boschwitz's performance or who refused to answer the question rose to its highest level, at 20 percent.

For Mondale, the fact that less than half the respondents considered him the front-runner cannot be entirely encouraging.

Next to Hubert H. Humphrey, Mondale has been the biggest name in Minnesota politics over the last three decades.

He was the state's attorney general, a U.S. senator, a vice president and was the 1984 Democratic presidential candidate. Since moving back to the state in 1987, he's been in the news as much or more than Boschwitz.