The Labor Department Women's Bureau, which was created in 1920 in the wake of women's suffrage as a watchdog for the problems of working women, has fallen down on the job in the past three years, a House committee has charged in a new report.

The bureau, for decades a clearinghouse for publications, technical assistance and legislative data, has sharply curtailed its work and "has shut out a great many of its traditional and natural allies," including unions and women's and minority groups, according to the 20-page report by the House Government Operations subcommittee on manpower and housing. The full committee voted unanimously to accept the study.

"Despite administration proposals to cut the Women's Bureau staff year after year, Congress maintained the bureau's budget," said Rep. Barney Frank (D-Mass.), the subcommittee's chairman. "We recognize the importance of this small agency as the sole federal office devoted to the complex needs of the rapidly growing female workforce."

Bureau director Lenora Cole-Alexander, a former vice president of the University of the District of Columbia and American University, yesterday dismissed the report as "a political action without any substance" and said the bureau has been aggressively promoting expanded child care, job training and other concerns of women workers.

The report was based on hearings in July at which witnesses criticized the bureau on a variety of fronts.

From 1981 through mid-1984, the report said, the bureau published 11 publications, containing 27 pages of economic and employment information. By contrast, the Carter administration bureau put out 33 publications with 110 pages of data and analyses. The subcommittee said the record shows "diminution of an essential service," which was "unanimously deplored by a wide diversity of witnesses."

Cole-Alexander said "I don't see where the quality is determined by the number of pages" and said the bureau published a 1983 Handbook on Women Workers that had not been published since 1975.

The report also pointed to the case of Madeline Mixer and Gay Plair Cobb, who had shared the job of bureau regional administrator in San Francisco from 1980 until they were fired in 1983 by officials who said that such an important job needed to be filled by one person. The report said job-sharing has been supported by federal personnel officials, so bureau officials "should practice what they preach."

The bureau's fiscal 1985 budget includes a $204,000 increase to add six jobs to its 79-member staff and this should result in "broader outreach" and expanded efforts, the report said. PENSION INVESTMENTS . . .

The Labor Department has initiated its first study of investment practices and the financial performance of pension plans covered by the Employe Retirement Income Security Act.

The study will measure the impact of ERISA on investment behavior, according to Robert A.G. Monks, administrator of the Office of Pension and Welfare Benefit Programs. REORGANIZING . . .

Meanwhile, Local 12 of the American Federation of Government Employes, which represents the department's 5,000 employes, has objected to the proposed reorganization of the Monks office.

Union President Michael Urquhart said Local 12 has filed a Freedom of Information Act request to obtain the department's studies on the proposal. The local said, among other things, that the reorganization would downgrade some employes and reassign others without regard to merit. The department is reviewing the union's objections.