Senate Finance Committee Chairman Bob Packwood (R-Ore.) said yesterday that his committee will go back to "square one" to try salvaging tax revision and would even consider cutting tax breaks for his home state's cherished timber industry.

"I'm not going to eliminate any possibilities," Packwood said in describing the agenda for closed-door panel meetings this week. "There's no point in saying, 'We're going to start from square one -- but. . . ,' " referring to members' affinity for tax breaks.

The panel stayed busy yesterday on a stalled U.S.-Canadian free-trade agreement, which will be first on today's agenda.

Packwood has said that when that is dealt with he wants to meet privately with the 20-member panel and set priorities for virtually redoing the tax-revision bill. So far, members have been voting to curtail few loopholes and preserve many.

Packwood said he may schedule weekend votes to produce a committee bill by early May, when he plans on returning home to campaign for the May 20 primary.

Packwood said he plans to ask members to set three goals: how much they want to reduce tax rates, how much of the tax burden should shift from individuals to corporations and how many poor persons should be dropped from tax rolls.

Packwood's tax proposal, legislation passed by the House late last year and President Reagan's original tax plan each would cut the top tax rate for individuals to either 35 percent or 38 percent -- from the present 50 percent, would shift more than $100 billion in taxes over five years from individuals to business and would wipe out tax bills of more than 6 million low-income taxpayers.

Getting members to agree to such broad goals, Packwood said, might give them an incentive not to propose costly amendments that make it harder to reach the goals.

"I think once we start on the private meetings we will either move expeditiously or we won't move at all," Packwood said. He added that he thinks that the panel will approve a bill, perhaps one scaled down from his proposal.

However, some committee members continue to question whether the panel has the will to produce a sweeping tax-code rewrite, even in closed session.

During its first 11 days of tax-writing, the committee agreed to amendments that reduced the bill's projected revenue collection by $29 billion over five years.

"The prospects don't look good at all, as far as resolving it," Sen. Lloyd Bentsen (D-Tex.) said. "At this point, I don't see a consensus, even behind closed doors."

Sen. David F. Durenberger (R-Minn.) said the only way to meet Reagan's highest priority -- lowering the maximum personal rate to 35 percent -- is to adopt a bill with few deductions and credits. He promptly said he cannot envision that happening.

Sen. Bill Bradley (D-N.J.) praised the idea of meeting in closed session and making tough choices.

"It's not as if all this effort we've made in the last two weeks hasn't been helpful," he said. "You've got to go down an alley to find it's a dead-end."