The Reagan administration is taking steps to ban importation of Libyan oil to the United States and halt sale of U.S. oil production equipment to that country, informed sources said yesterday.

The oil boycott, the next phase of a U.S. campaign against Libyan leader Muammar Qaddafi, is expected to take effect within a month following discussions with U.S. oil companies, European nations and members of Congress, according to a knowledgeable source.

Another source said final decisions still depend on "things to be done" in the days ahead, an apparent reference to the consultations. White House spokesmen had no comment.

The economic actions, especially the oil boycott, have been under discussion for several months. They were the subject of widespread public and political speculation late last year amid administration reports of a Libyan "hit squad" directed against top U.S. officials.

There was no indication that the latest U.S. action was prompted by a renewal of "hit squad" reports or any other recent steps by Qaddafi. The new measures continue a long-term Reagan program of opposing Qaddafi who, the administration charges, has been supporting international terrorism and working as a surrogate of the Soviet Union.

First word of the decisions came from Middle East Policy Survey, a biweekly newsletter published here. The newsletter says, in a story being published today, that the decisions were made yesterday afternoon in a meeting of the National Security Council.

Libya, once the third-ranking source of imported oil for the United States, is now a relatively minor source, providing about 150,000 barrels daily in the present oil glut and U.S. recession. Oil industry experts said yesterday that a U.S. boycott would not be likely to cause major difficulties for the U.S. economy at this time.

By the same token, it was uncertain that a U.S. unilateral boycott would have a serious economic effect on Libya, since its oil could be sold elsewhere.

The political effect in this country and inside Libya could conceivably be greater than the economic impact. "Some serious opposition may be developing to Qaddafi internally," said Henry M. Schuler, a Washington economic consultant and expert on Libya. "An action such this could give a signal to those within."

Secretary of State Alexander M. Haig Jr. reportedly told senior associates in a staff meeting Jan. 18 that it might be time "to go to Phase II" of the anti-Qaddafi program, which would involve the U.S. boycott of Libyan oil.

At the same meeting, Haig was reported to have said that in early February Americans would be out of Libya and it would be time to consider another military exercise near Libya.

However, there was no report yesterday that the administration has decided on such an exercise. Two Libyan planes were shot down by U.S. fighters during a U.S. naval exercise in the Gulf of Sidra off Libya last August.

About 2,000 to 2,500 Americans, most of them connected with the oil industry, were reported to be in Libya last summer. Last Dec. 10, following several National Security Council meetings on the issue, the administration redoubled its appeals for Americans to leave. At that time, about 1,500 Americans were reported in Libya.

After the appeals, most of the American oil workers were pulled out. Only about 400 Americans remain, according to official sources, and it appears doubtful that most of them will leave voluntarily.

In today's slack oil market, there does not appear to be much that Qaddafi could do on the petroleum front to strike back at a U.S. boycott, according to oil industry sources.

Qaddafi reportedly has sought to arrange an Arab oil embargo of all petroleum sales to the United States as a visible and powerful gesture of support for him in the struggle with the Reagan administration. But there is no sign, according to the sources, that he is gaining converts to this proposal.

Another factor that may tend to reduce the chance of an explosive reaction by Qaddafi, according to sources, is that he is to become president of the Organization of African Unity this summer and thus is likely to avoid actions that could alarm African nations.

Qaddafi recently withdrew Libyan military forces from Chad at the OAU's request. One problem for the United States may be explaining why actions are being taken against Qaddafi in the wake of the withdrawal.

A ban on exportation to Libya of oil production equipment, including replacement parts, would tighten substantially the U.S. restrictions in this field.

But an industry source said it might make "not a lot of difference," other than perhaps forcing Libya to pay more for the same equipment and parts from other sources on the worldwide market.