Big cities, which spent as much as $145 million of their own scarce money on the arts last year, may be getting considerably more help from the federal government soon.

The National Council on the Arts took a first step in that direction yesterday after being told by the staff of the National Endowment for the Arts that the rapid proliferation of local arts agencies has created such a need.

The Council, which includes many famous names in the arts and philanthropy, is an advisory board to the Endowment.

If the subsidy proposal goes into effect, it would be the first time the Endowment has contributed to communities' art operating costs and given the cities discretion over how to spend the money. The Endowment has given money on a similar basis to the states for 10 years.

Figures in this area are elusive, but local arts expenditures are already estimated by the Endowment staff virtually to equal state and federal contributions combined.

In some cases the municipal burden far exceeds the state's. In Pennsylvania, for instance. Philadelphia last year budgeted $18 million for the arts while the state appropriated only $1.6 million, and the state had federal help.

Henry Putsch, who runs the Endowment's Office of Federal-State Partnership, said yesterday that the cities' councils now operate on an ad-hoc basis. He appealed to the Council to "recognize what is happening at the local level and get a handle on it while we still can."

Pressures for help have been growing from the municipalities because many of them are in severe financial straits. Their spokesman, John Blaine, director of the Seattle Arts Commission, declared yesterday that local government arts financing "has reached the point where we must decide if we are going to work with the federal government or whether we leave them alone."

After about four hours of testimony and discussion, the Council instructed the Endowment staff to prepare a detailed proposal on which the Council could vote by its November meeting. Included would be such issues as eligibility, the extent of the federal contribution and control, and the range of programs that might be included.

This financial relationship with communities would supplement the existing arts spending partnership between the Endowment and state arts councils. Since its inception in 1967 the Endowment has poured about $100 million into state programs. State appropriations also have risen from $4.8 million in fiscal 1967 to a projected $70 million in fiscal 1978.

Meanwhile, it may well be that local expenditures have been growing at an even faster pace, without federal aid. The Endowment says that governmental financing of the arts is now in the range of $300 million yearly - with $85 million from the Endowment, $70 million from the states, and the rest from localities. Their figure is somewhat complicated, however, by the fact that municipalities have received federal grants for special programs in the past, and also by the exclusion from this fiure of money from the Labor Department, the General Services Administration, the Commerce Department and HEW that might be construedas arts financing.

The need for financial relief is probably greatest in the financially beleaguered cultural centers of the East. But the intensive municipal investment in the arts seems to be happening all over the nation.

At the Council meeting, which was held at the Mayflower, when some raised the question of how much the program would cost, jazz pianist and Council member Billy Taylor replied, "Big."

No outright opposition to the plan was expressed by any of the Council's 26 members. The closest it came to that was a remark by Richard F. Brown, head of Fort Worth's Kimball Museum, that "we should build on what we've got as much as possible."

Putsch pointed out to a reporter that under the proposal the Endowment would serve, also, as a coordinator among the proliferating organizations and as a central clearing house for information. The effect should be more "informed decisions" at all levels, he said.

Yesterday's recommendation results from a year-long reassessment of the Endowment's federal-state programs by a task force that conducted hearings in numerous locations and documented the conslusions in a 110-page reports.