The Phillips Brooks House Cabinet voted Sunday night to endorse the opposition slate for the Coop Board of Directors, reversing a PBH policy of not taking stands on public issues.

"This is one time when the issue--working with the community--is something PBH has expertise in," Joan S. Rubin '69, PBH secretary, said yesterday in explanation of the change.

In its resolution of support, the Cabinet said: "This slate of directors will be able and willing to direct the Coop to bring about changes of policy which PBH feels are of vital interest to its own concern as a community oriented organization."

Recommended

The resolution also recommended that the slate, if elected, consider these actions:

* Investing in the Unity Bank and Trust of Roxbury, a move some members of the 16-man slate have already suggested.

* Creating a charitable foundation to which members of the Coop could contribute their rebates.

* Training and hiring community residents on a permanent basis.

* Setting up management training seminars for small businesses in Cambridge.

The resolution was passed with only one abstention and one opposing vote in a meeting of 20 people. The Cabinet is made up of the heads of each of PBH's 35 programs.