New York Gov. Hugh L. Carey told Congress yesterday that New York City still will need some seasonal borrowing help from the federal government in addition to the long-term loan guarantees the Carter administration proposes to give the nation's biggest city.

Carey said he welcomed the administration plan - advanced last week by Treasury Secretary W. Michael Blumenthal - but said that, when the current seasonal loan program expires on June 30, the city still will be without access to the market.

Blumenthal said the administration would be amenable to giving the city some sort of seasonal financing assistance.

Like many other governments - including the federal government - New York City's spending requirements are fairly constant from week to week, while it collects revenue in big chunks.

Sometimes it needs seasonal loans in its cash balance until its next tax collection date.

But the city also needs longer-term loans over the next few years to permit it to get its budget into a real - rather than technical - balance.

Felix Rohaytn, chairman of the state-sponsored Municipal Assistance Corp. set up in 1975 to do New York City's borrowing, said that, at least for the next few years, both seasonal and long-term borrowing help will be needed. He said the city may never need to tap a stanby seasonal line of credit.

"Without long-term assistance, the city cannot do any seasonal borrowing," Rohaytn said. Without seasonal help, it would not be prudent for investors to lend New York on along-term basis.

Carey and Rohaytn testified before the House Banking Committee Subcommittee on Economic Stabilization. Both said they welcomed the Carter administraion's proposal - the center-piece of which is $2 billion of long-term loan guarantees to the city for the next four years - as well as the administration's commitment to get New York help through Congress.

Although the House subcommittee, headed by Rep. William Moorehead (D-Pa.), is sympathetic to the city's difficulties, the overall House of Representatives is much less so. In the Senate all 15 members of the banking committee, led by Chairman William Proxmire (D-Wis.), have approved a report that said New York City could avoid bankruptcy without federal intervention.

Carey said that Proxmire is wrong, that without some form of federal help and guarantee of loans, the city and state pension funds would be unable to buy any more New York securities for fiduciary reasons.

Carey said that New York's financial difficulties are unique and that by helping the city the federal government would not be setting any dangerous precedents.

But, Carey warned, if New York City does go bankrupt, the impact on other states and cities would be disastrous. Borrowing rates would rise astronomically and some municipalities would be unable to borrow, he said.

By helping New York, "You are preventing an epidermic that could spread to your community," Carey said.