A Senate committee yesterday turned aside vigorous White House opposition and tentatively approved an amendment to President Carter's civil service revision bill which would broaden significantly protections given government employes who "blow the whistle on their bosses.

Instead of limiting these protections to employes who disclose illegal acts, the new wording would protect from such reprisals as firing or demotion any employe who makes public allegations based on a "reasonable belief" that an agency has engaged in gross waste, mismanagement or abuse of authority, or that the agency's actions endanger public health and safety.

Administration officials have objected to this degree of protection on the ground that it would "severely compromise" the presidents plan to make the bureaucracy more manageable and effective. They say it would "spawn a new form of personnel litigation" more formidable than the existing disciplinary apparatus that the president is trying to streamline.

Disgruntled employes faced with dismissal or demotion, or who disagree with a policy decision made at their agency, might turn themselves into whistleblowers in order to trigger such new protective machinery and block actions against them, argued Si Lazarus, a White House domestic policy official who sat in on the session.

However, according to one Senate source, the amendment made by the Governmental Affairs Committee "does not give an employe immunity if he's a lousy employe, if he's someone who doesn't work but spends all his time one the phone" to the press. "He's not protected either if disclosing that information is prohibited by law or an executive order on classified material," the source said.

Rejecting a White House compromise offer, committee chairman Abraham Ribicoff asserted that "some of the most horrendous examples" of government wrongdoing have been in the field of public health and safety, or other areas not covered under the administration bill's illegality standard.

He specifically mentioned recent reports that the General Services Administration spent large amounts of money near the end of fiscal 1977 so as not to endanger its future budget justifications.

In three markup sessions, the committee has, among other things, given formal approval to the president's proposed Senior Executive Service for government managers. The committee and the administration first agreed on compromises which set limits on the executives' pay raises, expanded the scope of the SES, and made other refinements and "cautionary" notations in the original language.