Business leaders greeted Ronald Reagan's election and the GOP's Senate takeover with excitement yesterday, lifting their hopes for major changes in government tax policies and regulations affecting business.

The stock market's post-election take-off yesterday reflects confidence by the business and financial community that should result in increased investment in the economy, said Reginald H. Jones, chairman of General Electric Co., one of the spokesmen for business' position.

"With this landslide sweep of a more conservative economy stance, you're going to see a considerable encouragement of the private sector," Jones said.

"We've reached a real watershed in this country," said William M. Agee, chairman of Bendix Corp. and head of Businessmen for Reagan-Bush.

Agee, like other business executives active in Reagan's campaign, believes his election will produce sharp reductions in the rate of growth of federal spending. "None of the [political] people in the recent past has been prepared or had the political courage to attack some of the root causes of inflation," said Agee, citing in particular the formulas that raise federal income support programs to match the gains in inflation.

"I firmly believe this administration will look much much harder at savings investment and encourage it. I fully expect us to look long and hard at some of the entitlements programs. Not that they will eliminate them, but they will make them more in accord with economic conditions," he said.

John Fery, chairman and chief executive of Boise Cascade Corp., said Reagan's "biggest challenge will be to lower expectations" after his one-sided victory and the Republican takeover of the Senate. "The country's problems are very large and will not be quickly or easily resolved," said Fery, an active Reagan supporter.

Fery said a Reagan administration will undertake a careful review of regulations affecting business. "I don't see major changes in goals or rollbacks. I do see a rationalizing of regulations to assure their cost-effectiveness.

"This country has come a long way in development legislation to protect and improve the environment," he said. The clock won't be turned back, Fery predicted, but businesses will be given more time and flexibility to meet the goals. "The objective will be to make sure we're spending the right money in the right places at the right time."

Malcolm Baldrige, chairman of Scovill Manufacturing Co. and chairman of the Reagan-Bush campaign in Connecticut, said the environmental laws are "something the people of this country have won." But a Reagan administration will strike a better balance between the costs and benefits of regulation, he said.

Baldrige said he thinks Reagan's controversial proposal to cut personal income taxes by 10 percent a year for three years will work. "It's worthwhile taking the risk," particularly when those reductions would merely ofdfset scheduled increases in Social Security taxes.

He also called for enactment of Reagan's proposal to establish "free enterprise" zones in depressed urban centers, giving companies tax incentives to establish new manufacturing plants there. That is the best aid that a Reagan administration could extend to minority groups, he said.

"It's a traumatic change. I feel very good about it," said Peter Johnson, a Boise, Idaho, business executive who headed the Reagan campaign among businessmen in the northwest.

"I see a liberation of the market system to do what it can to meet the economic and social needs of the country. I don't believe that all of our problems will go away overnight. That's not going to happen," he said. "But there will be a steady improvement in the environment for the free market system."

Jones and other business people said they believe Reagan will try to encourage business and labor to work together to seek common answers to economic problems. "The chances are very good that the dialogue between business and labor will continue," Jones said.