Senate Banking Committee Chairman William Proxmire (D-Wis.) yesterday cancelled a crucial hearing on proposed federal loan guarantees for New York City as labor negotiations between the city and its municipal unions broke down.

Treasury Secretary W. Michael Blumenthal, who has been pressing for orderly resolution of the city's labor and financial negotiations so that Congress can consider legislation for $2 billion in loan guarantees to the city before current federal assistance expires on June 30, said the situation was "now right down to the wire."

The hearing, scheduled for today, is a necessary preliminary before the full Senate can consider the loan bill which has already passed the House Banking Committee and which is being backed by the Carter administration.

Proxmire, who has been the chief congressional critic of further federal assistance to New York City, said he canceled the hearings "in view of the fact that no agreement has been reached on the labor contracts or on any of the other outstanding issues in the New York City financing situation."

The senator has set the hearings following a commitment made jointly by Mayor Ed Koch and Gov. Hugh Carey at a meeting two weeks ago with Blumenthal that the local parties would reach the necessary agreements for a new four-year financing package for the city by May 20.

"None of these actions have been accomplished to date," said Proxmire, though he noted "some progress has been made."

Blumenthal said he was "disappointed that the self-imposed deadline was not met. It is essential that the remaining issues be resolved quickly so that the hearing of the senate banking committee can proceed."

Koch canceled his scheduled trip to Washington and held a morning press conference where he predicted that Proxmire would hold the needed hearing in June, whether or not the city had reached new two-year contracts with its labor unions.

These contracts expire June 30 along with the current federal short-term loans to the city.

The city, meanwhile, faces a situation on Friday where it will run short of money to meet its bills if the city employe pension funds refuse to honor a 1975 commitment to buy another $700 million in bonds.

Koch said the city would meet its May 26 payroll, but said it was questionable whether the June 9 payroll could be satisfied.

The city is planning to delay payments of some routine bills, if that becomes necessary. And Deputy Mayor Phillip Toia confirmed yesterday that the city would withhold its May and possibly its June payments to the municipal pension funds. Tola said the city would also explore other short-term revenue sources, such as advances in state and federal aid.

With the Saturday deadline now passed and the Washington hearings no longer looming, the pressure that had built up to reach quick settlements not only in the union talks but in Albany on two key bills involving the city's finances and with financial institutions on commitments to buy more city bonds seemed to dissipate.

Koch and Carey, seeking to regain the lost momentum, met yesterday afternoon to plot strategy.