Monday night in Kansas City, Senate Majority Leader Robert J. Dole (R-Kan.) drank cocktails and talked taxes with 125 leaders of such home-grown companies as Faultless Starch and Pizza Hut.

In Omaha next week, Rep. Hal Daub (R-Neb.) will sit down to a menu of taxes and scrambled eggs with officers of Omaha-based Baker Supermarkets, local truck lines and an array of other business folk.

Be it breakfast in Boise with Sen. Steve Symms (R-Idaho), a tour of suburban Tampa real estate developments with Rep. Sam M. Gibbons (D-Fla.), or lunch in Austin with Rep. J.J. (Jake) Pickle (D-Tex.), the August agenda will be the same: taxes.

Lawmakers may have said good riddance to Washington tax lobbyists when they departed last week for their August recess, but the high-stakes corporate crusades for and against President Reagan's proposal to overhaul the tax code have gone home with them.

"If I were a member of the House Ways and Means or Senate Finance committees, I don't think I'd go within 100 miles of my home," said Lawrence J. O'Brien, a Washington tax lobbyist whose clients generally support Reagan's package. "There are legions of organizations that have concocted these let's-bite-him-in-the-ankle-when-he's-home routines."

Since Reagan unveiled his proposal to curb numerous popular tax deductions in return for reduced rates, opponents of the plan have dominated the debate with lengthy congressional testimony, dismal forecasts and a phalanx of lobbyists warning of economic collapse.

But the drama so far has been centered in Washington. Now lawmakers are taking soundings at home, and what they hear could affect developments next month when the Ways and Means Committee begins drafting a tax bill -- a point not lost on either side.

The Tax Reform Action Coalition of more than 100 companies and trade groups, the principal Washington lobby in favor of Reagan's proposal, has dispatched members who vote in the home districts of congressional tax-writers to meet lawmakers on their home turf this month.

The coalition, including small businesses, service industries, high-tech firms and a few large manufacturers with high tax rates, was responsible for the cocktail party with Dole and has a hand in the planned sessions with Symms, Pickle, Daub and others.

At one meeting in Grand Rapids, Mich., the chief executive officer of Gerber Foods and other local business leaders told Rep. Guy Vander Jagt (R-Mich.) that they consider the current tax code unfair, and would gladly trade existing tax breaks for lower rates, as Reagan proposed. According to one who attended, the message was:

"You've heard a lot from lobbyists in Washington who are against the proposal. We're your constituents and we're telling you we're for it."

"Lobbyists for the losers under the tax-reform bill are very well-financed, very well-organized and very active on the Hill," said Jeff Nedelman of the Grocery Manufacturers of America, a member of TRAC. "We believe the best way to counter it is to put elected representatives in contact with the grass roots."

Supporters appear to be fighting an uphill battle. Reagan's blueprint has languished for two months while congressional committees heard from hundreds of companies and groups that have prospered from tax breaks and want to keep them.

Once-favorable polls have begun to reveal dampening public enthusiasm, suggesting that the more Americans have learned, the less they like Reagan's version of tax reform. Some proponents even say privately that they do not expect Congress to produce a bill this year.

Many corporate lobbyists who once anticipated spending vast sums to fight the proposal are holding their fire. Real estate developers, life insurance executives and several manufacturers who oppose the plan said they will meet with congressmen, but will not mount a big offensive during the recess.

"There's not much constituency for tax reform per se," said lobbyist Charls E. Walker, who represents auto, steel and timber manufacturers opposed to the proposal. "Everybody likes lower rates, but voters don't like it when you say you're going to tax their health benefits, tax their life insurance, take away their state and local tax deductions."

Nonetheless, supporters of Reagan's plan insist that it is very much alive.

House Ways and Means Committee Chairman Dan Rostenkowski (D-Ill.), the chief congressional advocate of tax overhaul, predicted from the start that summer would be a low point in Washington. He told members of his panel in a letter last week to heed what they hear from the grass roots, rather than taking the word of lobbyists.

Initial soundings from the tax-writers' home fronts indicate that attitudes there are more fluid than polls or lobbyists have conveyed.

Rep. Robert T. Matsui (D-Calif.) met in his district with sheet-metal and air-conditioning contractors after their Washington lobbyists said they would be hurt by the tax proposal. But after devoting half of his speech to the president's tax plan, Matsui was asked no questions on the subject.

Rep. Willis D. Gradison Jr. (R-Ohio), who has met with dozens of local groups, said his district has emerged sharply divided: machine-tool companies opposing Reagan's proposed repeal of the investment tax credit, Federated Department Stores of Cincinnati willing to give it up for a lower rate. In division, says Gradison, there is freedom.

"Where your constituency is divided, it gives a member more flexibility," he said. " . . . I can't keep both groups happy unless I resign from the Ways and Means Committee."

As such, lobbyists favoring the proposal said they hope only to neutralize the opposition of the last two months, not to overwhelm it. Once Congress returns to Washington, where the president and Ways and Means chairman favor overhaul, the proponents wager, a divided constituency may be enough to push a tax-writer into Reagan's corner.

It remains to be seen whether Congress will trust the grass-roots pleas, or view them simply as orchestrated, down-home versions of Washington lobbying.

The insurance lobby learned this the hard way, after spending more than $5 million and generating 1.6 million pieces of mail to lawmakers opposing proposals to tax employe fringe benefits and the increased value of life insurance policies -- known as "inside buildup." Many tax-writers called the campaign overkill.

"A fellow from Texas can tell the difference between grass roots and Astro Turf," Sen. Lloyd Bentsen (D-Tex.) said of his mountain of cards and letters from opponents of the insurance provisions. "This is generated mail."