President Reagan's economic aides are "puzzled" and "confused" about the persistence of high interest rates, but there is no inclination in the administration to relax the tight monetary policies that have helped push interest rates upward, a member of the White House Council of Economic Advisers said yesterday.

William Niskanen took a pessimistic view of future interest rate levels in a discussion with reporters, saying he would be surprised to see long-term rates decline by more than one percentage point a year in the foreseeable future. That would mean continued weakness in the long-suffering housing and auto industries and some restriction on business investment, he said.

At the outset of the new administration, Reagan economic advisers has hoped that a fast start on the president's budget and tax programs would trigger a burst of confidence in the financial markets, leading to lower inflationary expectations and, as a result, a moderation in the real interest rates that reflect the markets' outlook on inflation.

That has not happened, although the Reagan economic program has moved faster than its authors had dared hope. Real interest rates -- the difference between market rates and the rate of inflation -- are unusually high. While inflation is believed now to be below 10 percent, rates on Treasury bills are above 15 percent, and this gap of 5 to 6 percentage points -- the "real" interest rate -- is about twice normal levels.

"We are bothered by that, and we are also confused," Niskanen said. "I think we should acknowledge that we are puzzled," he added, relating

Clearly, the administration has not yet persuaded investors in the bond market that inflation is being conquered, Niskanen said. "People don't change their expectations of long-term inflation very fast," he said. They also need to see a continuation of restricted monetary growth for some time if they are to believe that the corner has been turned on inflation, he added.

"It's better not to switch now, but to continue a slow money policy to cool inflation," he said.

There is a consensus among administration economists to "stay to course on monetary growth" although it is based "more on confusion than conviction. We have agreed on a policy from different perspectives. Different people for different reasons are supporting a common policy" of restrained monetary growth, even though it has increased the risk of a new recession, he said.

On other points, Niskanen sharply criticized the "all savers" amendment adopted by the Senate Finance Committee, which would create special, tax-deductible savings certificates to encourage greater investment in savings and loan institutions and banks.

It is "one of the worst ideas I've seen in public life for a long time," he said. "I see no reason why it would increase savings."