Treasury Secretary G. William Miller yesterday delivered an impassioned defense of the Carter administration's economic policies, but he limited the praise to his own 14 months in office -- pointedly excluding what went on before.

In a breakfast meeting with reporters, Miller initially lashed back at suggestions that Carter had waffled on economic issues. "What vacillation?" he shouted at one questioner. "We've been absolutely constant."

However, the secretary indicated later he was limiting his defense to what he called "my regime" in office -- which began in August 1979 -- and could not vouch for what the administration had done in previous years.

Asked, after criticizing former President Ford for failing to lift oil price controls, about Carter's own opposition to decontrol in 1977-78, Miller replied he was "not familiar with" Carter's stands before his own tenure began.

"There were at that time some learning curves -- I don't deny it," the secretary told reporters. He pointed out that Carter himself had admitted that the administration had overstimulated the economy during the first two years.

The secretary made his remarks before embarking on two political campaign trips -- one to Texas, scheduled for Friday, and another to New York next week. Miller will make speeches in both places.

He said he hadn't made "any political speeches out of town" before this. Tradition holds that the secretary of the Treasury avoid political speech-making, although this has been violated in the past.

Miller also honed his recent criticism of the Federal Reserve Board, saying he wished the Fed had been as reluctant to slow the growth of the nation's money supply in recent weeks as it was to speed it up last spring.

He said if the central bank could hesitate to bring money-supply growth within its target ranges "in one direction, why can't they hesitate another week or two in the other direction?"

The secretary's criticism referred to recent actions by the Fed to tighten money and credit conditions after it discovered that money-supply growth had far exceeded its previously set targets.

Money-supply growth fell below the Fed's targets briefly last spring, but the central bank did not move then to counter the situation, in part because of fears that it might revive inflation psychology.

The financial markets have been jittery at each new sign tht monetary growth is outstripping the Fed's targets in the belief that excessive money-supply growth only exacerbates inflation.

The sharp surge in interest rates last spring -- in which the prime rate soared to a record 20 percent -- was brought on in part by investors' panic over the prospect of heightened inflation.

The Carter administration, however, has been critical of the Fed's recent stand on grounds that too sharp a rise in interest rates might choke off the fledging recovery. Sales of new homes already have suffered somewhat.

Miller said yesterday he believed the Fed should move beyond "mechanistic adherance to regulating the money supply."

At the same time, he stopped well short of suggesting that the Fed abandon the new monetary policy approach it began in October 1979, under which it tries to concentrate on money-supply growth rather than interest-rate levels.

"I don't believe, after a year, that's a sufficient period to judge," the secretary told the group.

The Treasury secretary also made these points:

He dismissed warnings that the economy may fall into another, albeit milder, slump in part as a result of the rise in interest rates recently.

He reiterated that the administration may abandon its current wage-price guidelines program if Carter is re-elected and propose replacing it with new tax incentives -- or penalties -- designed to spur moderation in wages and prices.

He predicted inflation would remain high for several more years.