A federal judge here yesterday blocked Federal Trade Commission Chairman Michael Pertschuk from further consideration of an FTC ban on television advertising aimed at children.

In his ruling, U.S. District Court Judge Gerhard A. Gesell said Pertschuk had already unfairly made up his mind that the bank is necessary.

Gesell's strongly worded opinion said Pertschuk has effectively disqualified himself "by his use of conclusory statements of fact, his emotional use of derogatory terms and characterizations and his affirmative efforts to propagate his settled views."

Gesell said that for Pertschuk to continue to consider the ban (would render the [FTC] proceedings void and irrevocably tainted."

The judge's order, sought by three national advertising industry groups, the Kellogg Co. and the Toy Manufacturers of America, is unusual in that federal judges rarely block U.S. officials from participating in agency decisions. FTC general counsel Michael N. Sohn said it was the first time since the early 1970s that an FTC commissioner has been ordered off of a case.

Gesell said it is a sound rule that judges let the federal administrative process work its will. But he said that the groups seeking the ban on Pertschuk's participation in the children's television advertising case had made a "substantial showing" that his consideration of the issue "will and does violate their constitutional entitlement to due process."

Pertschuk has made repeated statements in interview, letters and public speeches that "children's advertising is inherently unfair" because youngsters are not mentally capable of understanding the commercials' intent to sell products.

But the FTC chairman, a former chief counsel for the Senate Commerce Committee, said again yesterday that, despite hie earlier pronouncements, "my mind remains open on the important issues raised" in the FTC rule-making procedure.

Pertschuk said it would be up to the five-mamber commission to decide whether to appeal Gessel's ruling. But his removal leaves only three commissioners - Elizabeth Hanford Dole, David A. Clanton and Paul Rand Dixon - to consider the controversial children's television advertising ban.

The fifth commissioner, Robert patofsky, had already withdrawn from the case because he once was chairman of the board of the Institute for Public Interest Representation, one of the two groups that initially petitioned the FTC for the rule-making proceeding.

Among other things, the proposed ban would block any TV advertising aimed at children too young - generally those under 8 - to evaluate the ads. Television advertising for those foods thought to cause dental cavities - mainly candy and presweetened cereal eaten between means - would be banned on programs seen by a "significant portion" of children under 12.

The proposed rules also would require that ads for less sugary or less risky foods be balanced by nutritional and health disclosures financed by the advertisers.

The FTC is accepting public comments on the proposals, and has scheduled public hearings in San Francisco starting Jan. 15 and here starting Feb. 15.

Commisioners of federal regulatory agencies are frequently strong advocates on one side or another of controversial issues, particularly before they are appointed to be regulators.

But Frederick P. Furth, a San Francisco attorney representing the Kellogg cereal producer in the FTC case, said that producer in the FTC case, said that Pertschuk had oversteeped his bounds as an FTC commissioner.

"Michael Pertschuk still thinks he's on Capitol Hill and he's still legislating," Furth said. "There's nothing wrong with Pertschuk coming forth and saying there's a controversy and I believe the FTC ought to investigate. But his job is to be a judge in these cases."

When the case was argued before Gesell Wednesday, Furth told him that the FTC case "needs a nonbiased, nonprejudged judge," Gesell told FTC counsel Sohn that he disqualifies himself in court cases "on the basis of [an] appearance" of a conflict in his ability to decide a case fairly.

The case is crucial to advertisers for a simple reason: they spend about $500 million annually on TV commercials aimed at children. The FTC hopes to determine in its public hearings the degree to which the quantity or quality of children's programs would be affected by a partial ban on ads, as well as whether the ban would violate advertisers' constitutional rights.