The chairman of the National Labor Relations Board yesterday failed to persuade several House Democrats that his personal politics were not behind the board's recent decision to strip its independent general counsel's office of powers it had held for 28 years.

Donald L. Dotson also was forced to defend his decision to let an aide continue to represent a plaintiff in a suit filed against a labor union and financed by the National Right to Work Committee while the aide was working with Dotson at the Labor Department.

During nearly four hours of often unfriendly questioning, Dotson tried to defend his claim that the board has reorganized the general counsel's office because agency lawyers had engaged in "sleazy" and "high-handed" conduct and had misrepresentated board opinions to appellate courts.

But he was unable to cite any specific court cases. And when he insisted that the entire board had been concerned about the situation, the members sitting behind him at the witness table disagreed.

Howard Jenkins Jr., who has served on the NLRB for 20 years and who was described by Dotson as the member who was "most upset" by misrepresentation, testified that he could think of only six cases out of the last 40,000 in which attorneys may have misrepresented the board. Jenkins said those cases involved a difference of "nuance," not blatant misrepresentation.

A transcript of the board's May meeting where the changes were discussed quoted Dotson as calling for a major reduction in the general counsel's powers, saying: "I'll make no bones about it. We are taking under this proposal substantial charge . . . I'm not interested in cosmetic change . . . ."

Board member Don A. Zimmerman, an independent appointed by President Carter and the only member to vote against the changes, told the committee that he was unaware of any discussion of a sweeping reorganization of the general counsel's office until one hour before Dotson proposed it.

Rep. Steve Bartlett (R-Tex.) tried to come to Dotson's aid several times during the hearing, saying at one point, "It seems we are looking for a smoking gun, and I fail to even see any smoke."

But Rep. William L. Clay (D-Mo.), chairman of the labor-management relations subcommittee and Barney Frank (D-Mass.) chairman of the manpower and housing subcommittee, continued to criticize Dotson.

They said that Dotson had allowed Hugh L. Reilly, the board's solicitor and an aide to Dotson when they both worked at the Labor Department, to serve as a private counsel in a lawsuit filed against the Communications Workers of America. The suit was financed, they said, by the legal arm of the National Right to Work Committee, which had retained Reilly before he joined the government.

Dotson said that Reilly had been unable to "extricate" himself from the suit because no one else was familiar with it and that Reilly had an "ethical responsiblity" not to abandon his client. Dotson also said that Labor Secretary Raymond J. Donovan and Solicitor of Labor T. Timothy Ryan Jr. were "fully aware" of Reilly's actions and that the department's ethics officer also was aware and did not object.

Michael Volpe, a Donovan spokesman, said that the secretary asked his staff to "look into the matter" when he learned from an outside source about Reilly's participation in the suit. When a staff member questioned Reilly, Volpe said, Reilly volunteered to withdraw from the case.