Division between the Defense and State departments on how to deal with current Central American peace talks broke into the open yesterday over a Pentagon document questioning whether such a pact is enforceable.

In a month-old study released formally yesterday, the Defense Department argued that, if Nicaragua signs any pact similar to the so-called Contadora draft being negotiated and violates it steadily for three years, "an effective containment program" would require "a protracted commitment of U.S. forces" involving at least 100,000 men and between $6.7 billion and $8.5 billion a year.

But the State Department, which has drawn up its version of what enforcement would require, quickly said that report was "an internal study written under contract" and "has no standing as a U.S. government document." Spokesman Charles E. Redman said it was made public without authorization.

Fred C. Ikle, undersecretary of defense for policy and sponsor of the 12-page report, retorted that Redman was "plain wrong."

Ikle said the document "was not written under contract" but in "a joint effort" among officials in the Pentagon and other departments. Ikle, a prominent conservative thinker, said the report "was shown to senior people at State quite some time ago, and they agreed with it."

The dispute surfaced as the Contadora peace talks among El Salvador, Honduras, Costa Rica, Guatemala and Nicaragua move into their final stage aimed at meeting a self-imposed June 6 deadline.

Treaty terms covering verification and enforcement mechanisms are among the most delicate issues remaining for a summit meeting of those nations' presidents this weekend in Guatemala, along with arms levels and a timetable for implementation.

A White House spokesman sought to minimize the dispute, noting that the Pentagon study "talks about a September 1985 draft that is no longer on the table" and contained "a lot of ifs."

He said it was "an informal, internal study . . . background material, an interesting historical document" about past treaties that should be considered in thinking about the Contadora pact.

At the same time, 101 members of Congress urged President Reagan to back a Contadora agreement if one is reached that meets U.S. "legitimate security considerations."

Rep. Richard A. Gephardt (D-Mo.) said there is "a furious debate" in the administration over whether to back the pact. "They don't know what they want to do."

Rep. Lee H. Hamilton Jr. (D-Ind.), chairman of the House intelligence committee, told reporters that verification would be possible. "We have our own verification technologies, devices, so we can assure ourselves the Nicaraguans would not be violating any agreement," he said. In return, "we will permit the Nicaraguan Sandinistas to exist."

The Pentagon study was made available to the media a month ago, but The New York Times published an article about it yesterday. The report was subsequently released in a blue binding complete with official stamp.

Entitled "Prospects for Containment of Nicaragua's Communist Government," it analyzed "the likely consequences if the present Nicaraguan government signed a 'Contadora'-type agreement, but subsequently violated it."

It noted that other leftist governments violated treaties in Korea and Indochina and that "Cuba has not been contained, despite the efforts of seven U.S. presidents."

Hamilton said the report appeared to confirm the Central American perception that the United States wants to undermine the Contadora proposals, which at present would ban outside military advisers, limit military exercises and promote democratic reforms.

Ikle denied that, saying, "It's an effort to properly inform members of Congress as to what the consequences are of various options. They would complain afterwards if we sat on this."