While the immediate impact of President Reagan's proposed $973.7 billion budget on the credit markets appears to be minimal, experts said yesterday that congressional reaction to the package could significantly influence interest rates.

Wall Street economists and traders also said yesterday the president's proposal contained no surprises. They said the financial markets already had discounted the budget because of leaks.

But they warned that if Congress fails to go at least as far in cutting spending as the president -- whose plan leaves a $180 billion deficit next fiscal year -- there will be upward pressure on interest rates.

"The proposed budget is already discounted in the market so the real issue is how much of what is proposed is going to make its way through the legislative process and get signed into law," said Charles Lieberman, senior economist at Shearson Lehman Brothers. "It is sobering to look to the end of the decade and see the budget estimates of the administration, which contain incredibly large deficits."

Lieberman said the bond market is troubled by the uncertainty over congressional reaction. He said the proposed budget is "far from satisfactory" and implies high real interest rates in the future because of the large deficits.

Edward Yardeni, chief economist at Prudential Bache Securities, said if Congress does not go along with spending cuts of at least $50 billion, it will hurt credit markets, driving up interest rates. He said if Congress proposes higher cuts, the market would react positively, sending bond prices up and yields down.

But the attention given to the federal deficit by Wall Street experts is less than was the case only two or three years ago, Yardeni said. "They are so bored with hysteria about the deficit that they are focusing on other things like low inflation.

"At some point the deficit will have to be addressed, but economists have been saying that for two years running and we are all still alive and well, with the economy up and interest rates and inflation down," Yardeni said. "Every economist in his heart of hearts has this notion that the deficit can't keep going up, but we don't know when this will be the paramount concern of the credit markets."

Yardeni said the fear that government borrowing would "crowd out" private borrowing has become "increasingly less prevalent." He said one reason the bond market has been weak in recent days is that the government has planned a $19 billion financing this week.

One expert said there has been some disappointment in the bond market in recent days because the composition of the president's proposed budget cuts is not believed to be "credible." He said several investors were concerned that Congress would not be willing to go along with budget cuts such as those that would sharply curtail farm price supports, college student aid and Medicare, while increasing the military budget 13 percent.