Senate Republicans are to begin working today on a "menu of options" -- based on an across-the-board freeze of all federal programs except those for the poor -- that Senate aides said could reduce deficits by nearly two-thirds, to $78 billion, over the next three years.

This would exceed the deficit-reduction target that the White House set but has been unable to meet on its own.

But some of the proposals are highly controversial and are considered unlikely to be accepted by the senators in their effort to write an alternative to President Reagan's deficit-reduction plan before Reagan's fiscal 1986 budget is submitted to Congress early next month.

The staff-drafted "menu," as one Senate aide called it, includes a freeze on all programs except those such as food stamps that are directed at the poor. The freeze would include a one-year denial of cost-of-living increases for Social Security benefits.

It also includes many of the specific proposals for additional cuts, including elimination of some programs and drastic curtailment of others, that Reagan is expected to propose in his budget.

In addition, there is a list of other possible cuts, considered even more controversial or questionable in policy terms, that would reduce deficits further.

The "freeze-plus" set of options was drafted under the auspices of Senate Majority Leader Robert J. Dole (R-Kan.) and Budget Committee Chairman Pete V. Domenici (R-N.M.), although aides said neither of the senators has approved specific items.

Taken together, the options would reduce deficits from a range of $225 billion to $240 billion over each of the next three years to $156 billion in fiscal 1986, $126 billion in fiscal 1987 and $78 billion in fiscal 1988.

The 1988 figure is well below the White House target of just under $100 billion by 1988, a goal that is estimated to produce a balanced budget by 1990.

Unable to get there on its own, largely because of reluctance to make deep cuts in defense or to tamper with Social Security, the White House has indicated that it welcomes the Senate Republicans' effort to try to make up the difference.

This is the job they are to undertake today in a meeting of the Republican leadership and committee chairmen that is expected to result in at least some substantive decisions, according to Dole.

This meeting is to be followed by one at the White House Thursday for senators who did not attend Friday's session at Blair House, which resulted in the senators' decision to try to draft a budget of their own. Dole said Treasury Secretary Donald T. Regan and White House chief of staff James A. Baker III, who are switching jobs, have been invited to participate.

Asked whether the White House is in effect asking the Senate Republicans to make hard choices it is reluctant to make, Dole said yesterday, "I don't think there's any pushing. We just want to get it done."

In other budget developments:

* Administration officials said yesterday that the president's budget will not include proposals to freeze cost-of-living adjustments in the food stamp program, as tentatively planned earlier.

* Health and Human Services Secretary Margaret M. Heckler, at a meeting with the president last week, raised the possibility of maintaining the cigarette tax at 16 cents a pack instead of letting it drop to 8 cents on Oct. 1. She suggested using the money to help the financially troubled Medicare trust fund.

Aides said Heckler did not make a formal proposal but brought up the idea, which she has long favored, when asked where money to reduce the federal deficit could be found if certain program cuts she opposed were not made.