Opponents are about to open a new front in the battle over President Carter's plan to start draft registration this year.

Chairman Robert W. Kastenmeier (D-Wis.) of a House Judiciary subcommittee said yesterday that he will insist that the Carter administration disclose what it plans to do with 19-and 20-year-olds who refuse to register.

If the "hell no, we won't go" threat takes hold, the nation's courts and jails could become overwhelmed with these otherwise law-abiding young people, Kastenmeier said.

He said the administration will be asked about its plans for this possibility in hearings by the courts and civil liberties subcommittee he chairs.

Kastenmeier said his decision to conduct a subcommittee inquiry "comes in part from personal reservations" about peacetime draft registration.

Peacetime registration, he said, "is not any more necessary today than it was in September, when President Carter opposed it. It is divisive and leads to a whole series of decisions," including how to enforce registration laws.

In hearings on Carter's plan to require 8 million 19- and 20-year-olds to register, administration witnesses have said they do not anticipate any widespread refusal to comply.

The American Civil Liberties Union, an opponent of peacetime registration, estimates that at least 4 percent of those required to register, or 320,000 people, would not do so.

The law provides a fine of up to $10,000 and five years in jail for failing to register. Enforcing the law, according to David Landau of the ACLU, would overwhelm the nation's legal system.