The defeat of chairman Al Ullman (D-Ore.) and two other liberals on the House Ways and Means Committee has left the powerful tax-writing panel in disarray, with the possibility that it might alter colors dramatically in the upcomi [WORDS ILLEGIBLE] ss.

Not only is the committee's chairmanship now uncertain, but its core of moderate and liberal Democrats has been decimated by recent resignations or defeats. The result could be a far more conservative panel to deal with President Reagan.

At the top of the list is the question mark over who will succeed Ullman as chairman. Normally, the post would go automatically to Rep. Dan Rostenkowski (D-Ill.), the panel's current ranking Democrat, who is close to organized labor and a relative moderate on most tax issues.

However, with the defeat of House Majority Whip John Brademas (D-Ind.) on Tuesday, Rostenkowski is in line for the whip's job as well -- and may choose it as more prestigious and less demanding. The Chicago lawmaker was still mulling his options yesterday.

At the same time, the committee's Democratic ranks were reduced yesterday by the defeat of Reps. James C. Corman (D-Calif.) and Joseph L. Fisher (D-Va.), two other liberals on the Ways and Means roster. House leaders still have not decided who will fill their slots.

The panel's liberal minority already had been hit by the resignations of Reps. Charles A. Vanik (D-Ohio), who is retiring this year, and Abner J. Mikva (D-Ill.), who left Congress earlier to become a federal judge. Many of the newer Democrats are far more conservative.

Even with significant changes, congressional observers say, it's still far too early to say how fully the new Ways and Means panel will support the economic and tax policies expected to be proposed by the new Reagan administration.

"It's one thing to say they'll be more conservative," one source says, "and another to say they'll support the Kemp-Roth bill," the 10 percent across-the-board cut in individual income taxes that Reagan made the centerpiece of his 1980 presidential campaign.

Most economists, and many key conservative Democrats as well, see the Kemp-Roth proposal as fiscally irresponsible and likely to bring on more rapid inflation -- a view that seems to be shared by a good many voters, at least according to recent polls.

When Reagan unveiled his most recent version of the Kemp-Roth proposal in mid-July, Ways and Means Democrats continued to oppose the plan, while Democrats in the Senate drafted their own alternative plan based more on President Carter's tax-cut package.

Still, the new Ways and Means panel, whatever its stripe, is considered likely to show intensified support for such Reagan-supported proposals as faster depreciation writeoffs, intended to encourage more business investment, and larger tax-exemptions for interest and dividend income.

It also will be more likely to back such other conservative-supported measures as a tuition tax-credit for parents of college or parochial school students and possible further reductions in the income taxes imposed on capital gains -- profits from the sale on property or stocks.

As of late yesterday, House Democratic leaders were said to be pressuring Rostenkowski -- who is a close friend of House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) -- to take the Ways and Means slot, which is far more difficult to fill than the whip's job would be.

Rostenkowski, who was not available for comment yesterday, has been reluctant to take on so demanding and public a post. Although clearly adept at the kind of backstage politicking that is needed for the slot, he's described by associates as occasionally lazy. t

The most frequently proffered assessment on Capitol Hill of how Rostenkowski might fare as chairman of the Ways and Means Committee is that "Danny would be really good -- if he'd stay interested in the job." A 22-year House veteran, he's chaired a tax subcommittee for two years.

Apart from the issue of who will be the new chairman, the question of who will fill the three new Democratic vacancies on the panel is still to be answered by the House Democratic leadership. Seats on Ways and Means are widely sought after because the panel has so much power.