Rep. Robert T. Matsui (D-Calif.) knew it when three congressmen approached him separately last week and asked him how their personal finances would be affected by tax revision.

Rep. J.J. (Jake) Pickle (D-Tex.) knew it when Ways and Means Committee Chairman Dan Rostenkowski (D-Ill.) began forming six-member task forces to hash over tough issues before they were presented to the committee. And Rep. John J. Duncan (R-Tenn.), ranking Republican on the panel, knew it when the committee's compromises appeased many members who had worried about losing tax breaks popular in their districts.

The committee still has a long way to go before it can produce a rewrite of the tax code. But there is an increasing belief among committee members, hunkered down yesterday and today in a rare weekend session, that tax revision will emerge from these long weeks of deliberation, that it has acquired a momentum that transcends the many objections members have with the provisions of the bill.

"There is an undercurrent of despair and disgust, but there is a recognition we're on this treadmill and have to ride it until it's time to get off," said Rep. James R. Jones (D-Okla.). "There is a sense we're going to go down to the end of the line."

Action by the committee is the necessary first step for any major tax bill. But it is only one step that must be followed by action in the House, the Senate Finance Committee, the Senate and a joint conference committee. House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) has said he doubts the House can take up the bill this year as long as the body is tied up with budget matters. Senate Majority Leader Robert J. Dole (R-Kan.) has expressed similar doubts.

The committee will be hard-pressed to finish before Thanksgiving, as Rostenkowski hopes to do. But the panel has come a long way since its first weeks of tax-writing in early October.

Then, members had little idea which issues were coming up each day, or what amendments would be offered. Rostenkowski was rolled on several votes without warning, including an amendment that would have cut banks' taxes (it was later reversed) and a proposal not to tax workers' compensation.

"Those amendments probably would not pass today," Matsui said.

The change has occurred principally for two reasons: The task-force process has made members more personally committed to the final product, even if they oppose the results. And the substantive compromises have placated many who had objections.

Jones, for example, was chairman of the task force on pensions. He personally opposed several elements of Rostenkowski's plan, which curtailed such tax-favored retirement programs as Individual Retirement Accounts and "401(k)" tax-deferred savings plans.

"The task force was constructed so that if you wanted to make changes, you lost on a tie vote," Jones said. "Once it went into committee, we felt we should support it."

Rostenkowsi met for long hours Friday and yesterday working on the technical issue of taxation of income of companies with operations abroad and other foreign tax issues.

He generally prevailed in committee yesterday. An amendment by Rep. Sam M. Gibbons (D-Fla.) to strike all the proposed changes in the foreign tax area was defeated, 26 to 10. Nine Republicans and Gibbons voted for the amendment, which would have cost $13 billion in lost tax revenue over five years.

Other changes enacted yesterday would retain the existing tax credit for corporations with operations in Puerto Rico and other U.S. possessions, with some restrictions on its use. Reagan had proposed replacing the credit with one related to wages paid by those corporations. And the committee agreed to reduce the income Americans can earn abroad tax-free from $80,000 plus housing costs to $75,000.

Those actions, plus several new restrictions on use of the foreign-tax credit and the way companies can attribute income and expenses to their foreign operations, would raise about $12 billion from 1986 to 1990, $2.5 billion less than Rostenkowski had wanted and $1 billion less than the Reagan plan.

Rostenkowski also has met with informal coalitions of members interested in particular issues in an attempt to find compromises.

He told Rep. Beryl Anthony Jr. (D-Ark.), for example, that he would be allowed $800 million in tax revenue over five years in his efforts to curtail fewer tax benefits to the timber industry, and Anthony stayed within the limits. Rep. Wyche Fowler Jr. (D-Ga.) agreed to cut back an amendment extending a tax credit for solar devices to three years instead of five.

In the next week, Ways and Means will have to deal with such expensive and controversial items as repeal of the 10 percent investment tax credit and tightening of the minimum tax on individuals and corporations. The task-force approach will be put to the test then.

"All the big-money items lie ahead. It's a mine field out there," said Rep. Willis D. Gradison Jr. (R-Ohio).