Democrats on the House Post Office and Civil Service Committee have emerged from a series of more than half a dozen caucuses with what some say is working consensus of changes to be made in President Carter's civil service revision bill.

Those who have attended the sessions have been reluctant to discuss proposed changes. But one informed source reported that they include a provision for a "double election" form of union security (fee collections from nonmembers in a bargaining unit).

The Carter administration has termed that compromise "unacceptable," though officials have indicated that there are other compromises that they would consider.

The union security compromise would give federal employes a chance first to vote on union representation. If such a vote is favorable, they would vote again on whether to set up a so-called agency shop, in which all employes, whether union members or not, are required to pay a fee.

The union security issue is one of the more controversial items on a list of alterations being promoted by federal employes unions and their champions on the committee, Reps. William D. Ford of Michigan, William Clay of Missouri and Stephen J. Solarz of New York.

Another of those items did not make it into the working draft, according to the source. It would have given federal employes the right to a "pretermination hearing," which would be a hearing that must be held before an employee can be fired. The administration had vigorously opposed that proposal.

Also missing from the working draft, the source said, was a proposal to revise the Hatch Act, which prohibits public employes from certain political activity. One report held that Clay would try to get the revisions included at some point.

Key members of the Senate have indicated they would oppose passage of the Hatch Act revisions on top of the civil service revisions because the two together would "put too much politics into the bureaucracy."

The working agreement is not yet "written in concrete," as one committee spokesman put it, and could go through more changes next week.

But the Democrats had deemed that a consensus was necessary before they could proceed to a markup on the bill. These sessions are tentatively set for the week of June 19, according to a spokesman.

Aides also attended the caucuses described them as "unusually productive," with "all disagreements friendly and strictly on the merits," and with never fewer than 10 members present.