The Senate, taking a key step toward final implementation of a budget accord between the Reagan administration and Congress, approved early today a $26 billion package of deficit reductions that includes a $9 billion tax increase.

Passage of the measure occurred on a voice vote and sends to a House-Senate conference one of two bills needed to enact into law the Nov. 20 congressional accord with the White House that called for a minimum cut in the deficit this year of $30.2 billion. The Senate is scheduled to begin debate today on the second piece of legislation, an appropriations bill that contains further deficit cuts of $7.6 billion, a version of which has already passed the House.

Senate adoption of the deficit legislation, which grew out of prolonged negotiations between the Reagan administration and congressional leaders after the Oct. 19 stock market collapse, came against a backdrop of new financial tremors. The announcement yesterday of a record $17.6 billion U.S. trade deficit in October pushed the value of the dollar to record lows against other major currencies and caused wide price swings on Wall Street, where the Dow Jones Industrial Average closed down 47.08 points.

Approval of the leadership-backed measure, known formally as a budget reconciliation bill, occurred after the Senate handily rejected a more ambitious deficit-reduction package that would have limited cost-of-living increases for Social Security recipients and other government retirees and eliminated pay increases for federal employes.

The substitute package sponsored by Sen. Nancy Landon Kassebaum (R-Kan.) proposed to reduce the federal deficit this year by $41.3 billion by freezing tax rates and most federal spending at 1987 levels. It was killed 71 to 25.

The leadership-sponsored reconciliation measure ensures a $26 billion reduction through a variety of spending cuts, asset sales, user fees and $9 billion in higher taxes, primarily affecting corporations and wealthy individuals. Combined with $7.6 billion in savings from discretionary domestic and military spending called for the appropriations bill the Senate will take up today, the total package would trim the anticipated deficit by more than $33 billion, about $3 billion more this year than the accord calls for, and by $46 billion in fiscal 1989.

Though administration officials support most aspects of the leadership's reconciliation legislation, the White House has threatened to veto the measure unless some objectionable provisions are removed.

In a letter sent yesterday to Senate leaders, Treasury Secretary James A. Baker III and Office of Management and Budget Director James C. Miller III objected, among other things, to language enacting into law the "fairness doctrine" under which broadcasters would be required to air competing points of view on controversial issues, to farm provisions including a limit on loan rates and establishment of a new oilseed loan program they said would hurt U.S. trade policy, and to the amount of rural electrification and rural telephone bank loan sales.

Last night, the Senate removed the "fairness doctrine" provision, but language enacting the standard is still alive in the House's version of the spending bill. A provision calling for fees on the transfer of broadcasting licenses that the administration also objected to was removed from the Senate bill.

During debate, senators defeated, 53 to 41, an amendment that would have closed a tax loophole that allows large poultry producers such as Perdue Farm Inc. and Tyson Foods to defer millions of dollars in taxes each year. Although the bill prohibits large producers from using the loophole in the future, the amendment would have cracked down further, requiring collection of taxes already deferred.

Among those voting to kill the amendment were Sens. Paul S. Sarbanes and Barbara A. Mikulski, both Maryland Democrats.

Senate leaders who participated in the prolonged budget talks with top administration officials defended the pact as the only one that could pass both houses of Congress, even if it is not the optimum proposal.

Senate Majority Leader Robert C. Byrd (D-W.Va.), for example, characterized the leadership package as "an exercise in the practical, the doable, the attainable" that manages to break through six years of fiscal stalemate between the White House and Congress.

Byrd said the package was the only one that could eventually be adopted and was preferable to the alternative of deep, across-the-board spending cuts that the nation's balanced-budget law requires if Congress and the White House fail to agree to deficit reductions in specific areas.

Senate Finance Committee Chairman Lloyd Bentsen (D-Tex.) scoffed at those who urged more lofty efforts that he said had already been rejected as politically impractical by party caucuses in both houses.

The tax portion of the package would raise $9 billion in revenue through a host of minor corporate tax increases and the closing of an estate-tax loophole related to employe stock ownership plans. The only provision likely to be noticed by average taxpayers is one that would extend the current 3 percent tax on telephone bills, due to expire Dec. 31.

The bill also would impose Social Security taxes on tips, deny the child-care tax credit for the cost of sending a child to overnight camp and freeze the top rate on estate and gift taxes at the current 55 percent, rather than allowing it to fall to 50 percent next year as scheduled.

The corporate provisions raise revenue by speeding up collection of corporate estimated taxes and curbing the deduction for increases in funds reserved for vacation pay.

The Senate bill also would reduce the tax advantages of publicly traded limited partnerships, but it cuts less than the House tax-increase bill would. That bill, which has many provisions in common with the Senate but includes controversial provisions limiting deductions for home-equity loans and for mergers and takeovers, will have to be reconciled with the Senate plan next week.

The bill would achieve almost $6 billion in savings from a variety of federal programs, including entitlement programs that automatically confer benefits based on existing law. Among those savings are $2 billion from the Medicare program that provides health-care benefits to the elderly and disabled, $1.2 billion in farm subsidies and $1 billion in veterans loan programs.