Patricia Roberts Harris, the new Secretary of Housing and Urban Development, has decided to ask Congress to continue the Ford administration's community block grant program, a kind of revenue sharing for the cities, which is due to expire at the end of this year.

A top HUD official said Harris has also decided to continue HUD's primary housing assistance program for the poor, known as Section 8 of the 1974 Housing and Community Development Act. This program subsidizes the rents of poor families, who then have some freedom to choose on the open market where they want to live.

The HUD official said Harris has submitted a request to the Office of Management and Budget to increase HUD's 1977 and 1978 funding above the levels set by the previous administration. The budget increases would go to pay for more subsidized housing as well as for more aid to the cities under the block grant program.

The HUD official refused to say what the magnitude of the requested increases would be, but some HUD sources said Harris has asked the OMB to increase the 1978 block grant request from $3.5 billion to about $4 billion. If approved by the OMB, the increased funding levels would then go to Congress for its approval.

At a background briefing yesterday, the new HUD Secretary was determined to "fine tune" existing programs and stabilize the housing department rather than charge off in new directions.

The HUD official said Harris has decided that there is a need "to have a continuity in housing programs" rather than a "stop and go" pattern, as was the case during the Nixon administration, which in its early years went full throttle on subsidized housing programs and then suddenly placed a moratorium on them in 1973.

Harris and the Carter administration will seek to set reasonable goals for yearly subsidized housing starts and then develop programs to reach the goals, the HUD official said. In this regard, the official said the new administration will probably request money for additional public housing units in the 1978 budget. The budget submitted last month by President Ford for fiscal 1978 had no money for public housing.

In general, the official said, Harris believes that "there ought to be predictability" in the number of subsidized housing units built every year and that the number should reflect the needs of poor families rather than government decisions to stimulate or deflate the economy. Assisted housing "should not be used as a countercyclical tool," the HUD official said.

Asked whether the Carter administration will try a new approach to coordinating programs designed to aid deteriorating cities, the HUD official said Harris will call together other Cabinet secretaries from time to time to review federal urban policy.

But the approach - and the expectations - will be cautious. The HUD official said: "the Fairy Godmother's wand will not convert the urban cores into crystal palaces."

Meanwhile, it was learned yesterday that President Carter has tentatively approved the nomination of Jay Janis to be Harris' under secretary at HUD. Janis served as executive assistant to former HUD Secretary Robert C. Weaver between 1966 and 1969 and is a senior vice president for management at the University of Massachusetts.