The Carter administration's proposal to limit electronic eavesdropping for foreign intelligence purposes poses "substantial risks to the ability of the Department of Defense to provide intelligence information," the Pentagon told Congress yesterday.

The Defense Department nevertheless supports the administration's bill because it feels the intelligence risk is "balanced" by the need for safeguards against unnecessary wiretaps on Americans, said Adm. Daniel J. Murphy, deputy under secretary of defense for policy.

Murphy cautioned a House Intelligence subcommittee against amending the bill to put further restrictions on agencies. He said this would jeopardize U.S. security.

"The balance cannot survice if further burdens are added to intelligence operations by amendment in the course of the legislative process," Murphy said.

"It must be remembered that effective intelligence-gathering . . . is also necessary to protect the rights of Americans," he told the subcommittee on legislation.

The subcommittee yesterday began three days of hearings on four bills designed to regulate electronic surveillance for the purpose of gathering information about foreign intelligence activities in the United States. Spy bugging has never been regulated in this country.

Three of the four bills before the subcommittee, including the administration bill, would introduce the judiciary into the electronic eavesdropping process by requiring a warrant for all surveillance. The fourth bill would require prior approval of wiretaps by the President and the Attorney General.

The National Security Agency, a Defense Department organization that coordinates electronic eavesdropping, has admitted in testimony to Congress to intercepting communications of 1, 680 American citizens and groups over a seven-year period.

The practice was officially halted in October, 1973. Attorney General Griffin B. Bell said yesterday that no U.S. citizens have been the targets of bugs or wiretaps since he took office last year.

Bell said, though, under questioning from Rep. Robert McClory (R-Ill.), that foreign espionage activity in the United States is increasing. "We have opened our ports to Russian ships," Bell said, "and I have no doubt" that Soviet agents are entering the United States in greater numbers than before.

Both Bell and Central Intelligence Agency Director Stansfield Turner supported the administration bill yesterday.

Bell said the bill's safeguard guarantee that "no United States citizen or permanent resident alien could be targeted" for wiretaps or bugs unless there is good reason to believe he is involved in some kind of foreign intelligence activity.

Bell said there is a disagreement within the administration over the amount of information a judge should have when deciding whether to issue a warrant for electronic surveillance.

Vice President Mondale prefers a criminal standard under which it would have to be shown that a crime is being or is about to be committed for a wiretap warrant to be issued.

Bell said he does not think a criminal standard is necessary or practical. He said the evidence of intelligence activities the bill demands for wiretap approval is "tantamout to a crime. That's far enough, as far as I can tell. It's enough that I'd want to send him to the penitentiary."

Murphy, the Pentagon spokesman, proposed amending the bill to delete the requirement for warrants for electronic surveillance that involves only foreign nationals and no Americans.

Murphy also proposed deleting a requirement that judges be told what type of surveillance would be used, unless physical entry is contemplated.

The administration's bill already has been approved by the Senate Judiciary Committee. It is now before both the House and Senate intelligence committees.