Rose Fenstermacher says she gets angry thinking about big corporations and rich people who pay little or no taxes. And it irritates her that the tax code is so complicated.

But this businesswoman and true believer in President Reagan also says she's a little nervous about the tax-simplification plan the president came to promote here today.

"I don't overdeduct, but my deductions are important to me," said Fenstermacher, who runs an interior design business out of her home.

She would like to support the president but, fearing that her taxes might go up under the new plan, she said, "I'd rather stick with a system where I pay less tax."

Fenstermacher's sentiments appear common in this strongly Republican Philadelphia suburb, where "high-tech" computer and information firms lead natives to call it "Silicon Gulch."

Interviews with several dozen persons -- including a corporate executive, an elementary school principal, a retired couple, a hardware store owner and several secretaries in one of the high-tech firms -- indicate genuine support for the concept of a fairer, more simple tax code, but a certain wariness about how Reagan's plan might affect them.

"We live on pensions," said Eleanor Cairns, a retired teacher, as she waited for Reagan to arrive. "We like the idea of tax revision but we'll have to see what it does for us."

Those interviewed generally applauded Reagan's proposal to create a system with only three tax rates. They said they believed the current system is too complex and, because of its many preferences, is skewed toward the wealthy.

"If you have the money and the lawyers, you can get anything. It's the middle guy getting squeezed," said Horace J. Quann, who has run a small and cluttered hardware store on the main commercial street here for 50 years.

Many persons here provided examples to back up their belief that wealthy taxpayers avoid paying taxes. And they expressed hostility toward big corporations -- particularly those in the defense industry -- that they felt have not paid their "fair share."

Eunice Yanoviak, who said she and her husband make less than $28,000 a year running the Village Sandwich Shop, angrily likened corporations that pay little or no taxes to welfare recipients. "I'm tired of supporting the big corporations and everyone on welfare," she said. "I'll pay my fair share if everyone else pays their fair share."

Few said they felt burdened by the amount of federal tax they pay, only by the thought that they are shouldering some of the burden that rightfully should be carried by others.

They said the current system was so riddled with preferences that it encouraged people to stretch the law. But they also said they thought Reagan may have gone too far in proposing to eliminate the deduction for state and local taxes. Many said that would affect them significantly.

Ray Boyd, manager of a computer firm, said he approves of most of Reagan's plan. "But I don't like the no deduction for state and local taxes. That galls me. As far as I'm concerned that's double taxation," he said.

The Internal Revenue Service came in for its share of lumps, too. One woman called the IRS "a Big Brother" that she hoped would be less active if tax simplification were put in place.

Reagan's tax plan appears not to have generated intense interest outside of Washington.

"I'm interested but it's not a big deal for me. I'll still have to go to an accountant, I'll still have to pay an accountant's fee. I still can't do our taxes," said Elaine Cowchara, who with her husband owns Venus Nutrition in the Great Valley Shopping Mall here. With two grown children, they make $50,000 to $60,000 and she said she expects to continue paying about the same in taxes under Reagan's plan.

Cowchara said she had been expecting something more dramatic after all the talk of tax reform -- such as a flat tax on gross income "where you fill out a little slip of paper and you won't even need these millions of IRS workers any more."

But there was strong sentiment here in favor of trying to revise the tax system.

"I used to work in a bank and we'd order all the forms from the IRS at tax time and I just couldn't get over how many there were," said Rosalee Lukens, a secretary making between $20,000 and $25,000 at a high-tech company in the complex where Reagan spoke. "Right now you have to read books, you have to buy books just to understand what you have to do and even then you don't."

Jack Oppasser, an executive who lives in Malvern and commutes every day to a large Philadelphia chemical company, said he was a little concerned that the emphasis on tax revision, while needed, would allow the federal budget deficit to drop from sight as a problem.