The U.S. government, which runs the world's largest (free) speakers bureau, won't be sending any more forest rangers, nutrition specialists or foreign policy experts to talk with groups that exclude anyone because of sex or religious or ethnic background.

Federal officials have been barred for some time from attending conferences or participating in meetings at which persons are excluded because of their race. Now the White House has announced that the policy will be extended to cover sex, religion and national origin.

Thousands of government workers attend conferences each year as speakers, participants, observes or paying students. In many cases, they provide free, crowd-drawing talent that benefits the organizations involved and helps them attract other participants.

The new order could affect the incomes of restaurants, private clubs, fraternal organizations and conference and seminar centers if it is determined that they exclude anybody from membership or participation because of sex, race, religion or national origin.

Government exployees also are well represented at professional meetings and conferences and conventions, either as participants or students. In fact, an entire industry - conference arranging - has been built up or fleshed out, aimed at having meetings to which federal agencies will feel compelled to send paying people.

Federal agencies pick up the tab for employees who attend approved session. But they will no longer be sending anybody to any meeting or conference that is segregated in any form.

The broadened policy just now filtering down to federal agencies - was announced June 2 in a letter from President Carter to Alan Campbell, Carter's choice to head the Civil Service Commission.

CSC, among other things, sets the policies and guidelines followed by most other government agencies that employ 2.8 million people. Carter's letter to Campbell noted that the government rules now address only cases in which groups discriminate by race.

"It is this administration's policy," he wrote Campbell, "that federal officials should not participate in private conferences or meetings held in facilities which discriminate on the basis of sex, religion, or national origin, as well as race. Accordingly, I request that you take whatever action is appropriate to amend the abovecited provision to reflect this policy."