New York City is unlikely to get the increased federal aid it is counting on this year and should be required to make greater sacrifices than Mayor Edward Koch is planning, leaders of the Senate Banking Committee said today.

In a letter to Treasury Secretary W. Michael Blumenthal, Chairman William Proxmire (D-Wisc.) and ranking Republican Jake Garn (Utah) said that Blumenthal should get new commitments from New York before providing the second allotment of the $1.65 billion in federal loan guarantees which Congress approved last year.

They also urged that New York Gov. Hugh Carey be required to make a formal commitment of his willingness to provide at least the $200 million in additional state aid that city financial planners are counting on.

The senators asked Blumenthal to get formal word from the state of what other aid Albany intends to extend to New York City.

"Given that the state continues to run a surplus, despite a $750 million announced tax cut last year, it should be capable of further (aid)," Proxmire and Garn said.

New York should be pushed to make larger budget reductions sooner than it is planning to, rather than be allowed "to follow its more customary course of backloading such reductions into later years and hoping for the best," the senators said.

The city has pledged to balance its budget by July 1, 1981, under terms of the federal loan guarantee program. All the reductions of municipal jobs and programs are aimed at meeting that goal.