Richard Belisle, a telephone repairman, spent his lunch hour the other day in the Hennepin County Government Center, the city's largest monument to government excess, listening to the Republican Party talk about taxes.

It was a loud, well-publicized affair, with plenty of hoopla and breastbeating. The party had brought in two bands and some of its heaviest hitters from Washington to plug its lates rallying cry: a GOP-backed plan to cut taxes by one-third.

But Belisle wasn't impressed. "It's the same old stuff," he said. "Politicians are all alike. They all say the same old things."

This hit on the central prblem the GOP encountered this week when it moved across the nation in a seven-state tax-cut blitz. Simply put, could the party buy the public trust that it lost during the Watergate scandals by promising to cut axes?

Although the event was advertised on radio and in newspapers for two days, only 250 people showed up for the rally here Thursday. And that was the biggest crowd of the day.

Party Chairman Bill Brock's explanation gave insight into the problems that haunt the party and politicians in general this year.

"I haven't seen a good crowd in politics for six years," he said, "I really don't think the crowd is an indication of interest. I think the interest level is high."

Promising to cut taxes, of course, is one of the oldest, traditionally most effective political plays in the book. But convincing the public that Republicans can do it better than Democrates is something else.

Some simply don't like the GOP approach. "All they tell you is that they want to cut taxes," Ken Beitler complained here. "It's frustrating that they don't tell you what they want to cut spending money on. Is it national parks, cancer research or what?"

"It sounds like a meat-ax approach to me, a cheap shot", he added.

Republicans argue that they really don't want to cut anything, that their Kemp-Roth tax reduction act would cause an economic boom that would bring in more money than it would take away.

The proposal, named after its two chief sponsors, Rep. Jack Kemp (R.N.Y) and Sen. William Roth (R.Del.), would cut federal income taxes across-the-board by 33 percent over a three-year period.

By making the bill the cornerstone of their fall election campaign, the party is gambling that it will provide a convenient rallying cry against big government for Republican candidates across the land.

On on level, it works. For three days, the party's message and attacks on Democrats appeared on the television screens and in newspapers.

The party, so often split by internal strife, also displayed a veneer of unity. Yesterday morning in Chicago, for instance, former California governor Ronald Reagan told a press conference that there is "a distinct possibility" that he will run for president in 1980, and if he does he will run on a Kemp-Roth tax cut platform.

In a speech prepared fro delivery last night in California, Reagan's 1976 rival, former president Gerald R. Ford, also endorsed the proposal and called it the "Republican tax attack of "78".

Party regulars and congressional leaders were impressed by the tax cut blitz. "It's the first good thing I've ever seen the Republican National Committee do," said one former adviser to Reagan.

"At least it's a national plan. We're doing something together rather than having 435 people running around the country alone like scared rabbits," said House Minority Leader John J. Rhodes (R-Ariz).

The euphoria, however, coudn't mask the difficulties Republicans are having trying to sell themselves as the party of the taxcutters.

First, a host of GOP candidates have tax plans of their own and are reluctant to climb aboard the Kemp-Roth wagon. Then, there are the Democrats, unwilling to let the Republicans monopolize an issue.

In Minnesota, for example, where Republicans stand a chance of picking up two Senate seats, Democratic candidate Robert Short has a more radical tax cut plan than Kemp-Roth. To complicate matters further, his Republican opponent, David Durenberger, stops short of endorsing the Republican tax cut, favoring instead a proposal of his own that calls for a 20 percent tax reduction over two years with an inflation index attached to it.

A more serious problem is the GOP's image as the party of the fat cats. This was vividly brought out when Republicans, trying to promote a "tax cut for working people." landed at Chicago's O'Hare airport Thursday and were greeted by local party leaders riding in a Cadillac limousine.