President Reagan took his tax-simplification plan to "Main Street America" today, reviving his favorite antigovernment rhetoric and advertising the plan as a tax cut that "won't raise taxes."

Testing the themes that he intends to use in coming months to seek grass-roots support, Reagan portrayed his proposal as a rebellion against "oppressive" government taxation.

"Now is the time . . . to get the federal government off our backs and out of our way," he said in an address this morning against the backdrop of the Capitol in Colonial Williamsburg, where Patrick Henry heatedly denounced the British Stamp Act in 1765.

Today's federal tax system is breeding "discontent, disorder and disobedience," Reagan said. "It's a system that increasingly treats our earnings as if they were the personal property of the government, with decent citizens called before the Internal Revenue Service to answer for their income and expenditures and show their papers and their proof in a drama that is as common as it is demeaning."

Later today, in a speech warmly greeted by several thousand people here, Reagan struck a similar theme, asking the crowd to "remember how low you felt last tax day . . . as you prepared to sign that complicated document that turned over a big chunk of your income to bureaucrats you'd never even met."

"Our federal tax system is . . . utterly impossible, utterly unjust and completely counterproductive," he said. "It's earned a rebellion, and it's time we rebelled."

Reagan today repeatedly emphasized tax reductions in his plan and not offsetting increases for some individuals and businesses. Sen. Robert W. Kasten Jr. (R-Wis.) presented Reagan with OshKoshB'gosh overalls inscribed "Tax Cutter in Chief."

Reagan said his plan "won't raise taxes or increase the deficit. In fact, we call it America's tax plan because it will lower taxes and expand opportunities."

According to the White House, Reagan's proposal would cut taxes for 58.1 percent of American families, would mean no change for 21.2 percent and a tax increase for 20.7 percent. It would mean an overall tax-payments reduction of 5.2 percent by 1990 for individuals and a 22 percent corporate tax hike by then.

Speaking on the Winnebago County Courthouse steps, Reagan made no mention of his proposal to repeal the deduction for state and local taxes, which has stirred opposition in high-tax states such as Wisconsin.

Democratic Gov. Anthony S. Earl said this week that eliminating the deduction would be "terribly unfair."

White House officials disclosed that they have scrapped Reagan's planned visit to New York, another high-tax state where political opposition to his proposal appears to be intensifying.

Political director Edward J. Rollins said the White House "didn't want to start the campaign" for Reagan's plan "in a debate" with New York Gov. Mario M. Cuomo (D) over repeal of the state and local tax deduction.

Reagan used the Williamsburg motif today to expound on the theme that he is fighting the same "oppressive taxation" that motivated the Founding Fathers.

He said the current tax code "seems so rigged, so unfair, that it corrupts otherwise honest people by encouraging them to cheat."

"Thirty and 40 years ago, you didn't hear people brag at social get-togethers about how they got their tax bill down by exploiting this loophole and engineering that credit. But now you do.

"And it's not considered bad behavior. After all, goes this thinking, what's immoral about cheating a system that is itself a cheat? That isn't a sin, it's a duty," he said.

Reagan also argued today that tax simplification would make it more difficult for Congress to raise taxes in the future.

"If some Congress of the future gets it in its head to increase taxes, to raise the lowest personal tax rate from 15 percent to something higher, the public will immediately see what is happening . . . and they will rise up and resist, and they will be heard," he said.

Scattered protesters, some of them nude or topless, were evident here, demonstrating against administration policies in Central America. As he departed for Washington, the president said he did not see them, then added grinning, "I think I'm going to go back."

Responding to chants from another group, Reagan quipped, "I'm going to raise their taxes!"