You want to know how tough this tax bill vote today is for many Republican members of Congress? Consider the cases of two freshman members from opposite corners of the country, Dave Dreier of California and David O'B. Martin of New York.

Both are conservatives from conservative districts, instinctively pro-Reagan. But the president's Monday night speech in support of his $98.3 billion tax hike was not a big hit in these avidly pro-Reagan districts. At mid-day Tuesday, the calls to Martin's offices in the sprawling Adirondacks-St.Lawrence region of northern New York were running 21 to 2 against the tax bill Reagan was plugging.

While half a dozen calls seemed to come from a single group of senior citizens, and while a number of pro-Reagan calls came in later, making the ratio a bit less embarrassing, it was no one's idea of a mandate for higher taxes.

Still, it was better than the count in Dreier's suburban Los Angeles district, which went 189 to 24 against the bill.

And there were substantive political problems, too. Operators of hotels and bars in the Thousand Islands resort area of Martin's district were opposed to being saddled with the task of withholding on their waiters' tips. Investors and retirees in Dreier's district disliked the imposition of withholding on their dividends and interest.

So when Martin was called in Monday for a one-on-one with the president, and when Dreier had a similar session Tuesday with Reagan and Vice President Bush, they both came away uncommitted. But yesterday, the time for fiddling was growing short, and conflicting loyalties were tugging the two young Republicans in opposite directions.

Dreier says Lyn Nofziger, the former Reagan press secretary who was called back to White House service to lobby for the tax bill, "got me started in politics." Nofziger also got Reagan to campaign for Dreier two weeks before the 1980 election, in which Dreier won a narrow, 12,000-vote coattail victory.

When he complained about Nofziger's cigar during the meeting with Reagan and Bush, it was the sort of friendly joshing that old friends understand.

But Rep. Jack Kemp (N.Y.), leader of the anti-tax hike Republicans, is coming to Dreier's district next Thursday for a campaign appearance, and Dreier, like many of the other freshman Republicans, echoes Kemp's view of the tax bill.

"It's obvious this tax bill is not the answer," he said yesterday. "The only question now is loyalty. And I don't believe I am running away from Ronald Reagan; I'm steering him away from acting on bad advice. He was elected -- and we were -- on a platform that said we would balance the budget without raising taxes, and I think we ought to stick to that platform. So I'm leaning very much against the bill."

For Martin, the loyalty question is tugging the other way. Unlike others, he said yesterday, "I don't get very excited about this freshman class rah-rah stuff. The sooner we get our beanies off, the better off we'll be."

Martin has made the first step into the party establishment, as a regional whip, and he said yesterday that despite his concern about the paperwork burden the bill would impose, "I hope I can vote for a revenue measure that meets the goals of the budget resolution we passed."

Martin talked like a man who was leaning toward the Reagan position, but he cautioned a reporter not to jump to conclusions. "I'm uncommitted," he said, "and I'm going to take as much time as allowed to make up my mind."

To some colleagues, that translates as meaning that Martin will vote for the bill if his vote is needed for, and can assure, passage. But if it is going down to defeat anyway, he will spare himself the burden of explaining something that would plainly be unpopular with many constituents.

His position is not unusual on the Republican side, and it poses a problem for the GOP leadership. Democrats want to see Republican votes show up first on the electronic scoreboard "to calm some of the negativism that is making it hard to get votes for the bill on our side," as Majority Leader James C. Wright Jr. (D-Tex.) put it yesterday.

But few Republicans are enthused about the tax increase, and even fewer want to vote for it if it is a loser. The waiting game may make the last 15 seconds frantic. Still, there are many who just want the issue to be over, for it has divided the party and tested friendships and obligations as has no other issue of the Reagan presidency.

"I've spent more time agonizing about this bill than anything since I have been here," said Rep. James A. Courter (R-N.J.), a second-termer. Courter saw Reagan for 15 minutes yesterday. "He obviously was hoping for a commitment after the time he spent with me," Courter said, "but I told him I had not made up my mind."

Courter is torn. In June, facing a difficult primary, the staunch conservative got what no other Republican has received from the president: an endorsement in his primary fight. Courter is close personally to the leadership Republicans such as Rep. Dick Cheney (R-Wyo.), who are trying to save this bill for Reagan.

"But philosophically," Courter said, "it still looks to me like we're vacillating on the 1981 program and that is what concerns me -- even more than some of the specific provisions."

Rep. Charles Pashayan Jr. (R-Calif.) has been wrestling with the problem, not on philosophy, but as a lawyer worried about some of the provisions. Secretary of Agriculture John R. Block helped ease his fears about the impact on five big food co-ops in his district. Secretary of Defense Caspar W. Weinberger called to ask Pashayan's support.

But Pashayan said he was still "leaning against" the bill because of its withholding, pension and medical deduction features. So yesterday afternoon he was called over for his second White House session, and he said he was impressed by the force of Reagan's argument that deficit-reduction measures did seem to be bringing down interest rates.

When he got back to his office, Office of Management and Budget Director David A. Stockman was waiting to reinforce the argument about the need to reduce "the structural deficit."

"They want my vote," Pashayan commented drily. And do they have it?

"You could say I've moved from leaning against to undecided," he replied.

That's the kind of struggle it is.