Senators from oil-producing and consumer states agreed tentatively yesterday on a compromise oil "windfall profits" tax that would raise about $185 billion over the next decade, roughly $47 billion more than was proposed by the Senate Finance Committee.

Emerging from a third day of closed-door negotiations to break an impasse over the tax, Sen. Lloyd Bentsen (D-Tex.) told reporters there "seems to be a consenus" for a $185 billion target figure.

If the agreement holds, and there was no guarantee that it will, the Carter administration will be able to claim a substantial victory in its drive to push the Senate closer to the House-approved version of the bill, which would yield an estimated $277 billion by 1990.

An agreement among the chief protagonists in the windfall tax battle will presumably break a nearly week-long stalemate over an administration-backed amendment from Sen. Bill Bradley (D-N.J.) to raise the tax by $22.5 billion.

When Bradley's proposal appeared on the verge of passage last week. Republicans began a stalling campaign. This prompted Senate leaders of both parties, along with sponsors of major amendments, to begin groping for a compromise that would cover all or nearly all of the contested provisions.

The test vote on the Bradley proposal indicated that the administration and its consumer-state allies had the upper hand in moving to toughen the tax, although they had earlier lost a battle to the oil states over exempting most of the production of independent operators. However, oil-state senators and Republicans had demonstrated their ability to delay action, at least for the time being.

The compromise centers on the Bradley proposal plus a so-called "minimum tax" of 10 to 20 percent on various categories of oil that the Finance Committee proposed to exempt from the bill, including newly discovered oil and oil that is difficult and expensive to extract and produce. The Bradley proposal would raise the tax on oil discovered between 1973 and 1978 from 60 percent to the 75-percent rate that is already proposed for oil put into production before 1973.

Bentsen said details of the specific proposals had not been worked out as of late yesterday afternoon, when Republicans broke out of the bipartisan negotiations to caucus separately on the proposals. He said further meetings were expected today.

If an agreement among the principals in the dispute is nailed down, prospects for the bill's passage would be vastly improved, said Bentsen, adding that there is also the likelihood of a cloture petition to shut off further delay and hasten action on the compromise.