Henry A. Kissinger played both sides of the street in the 1968 presidential campaign, providing secrets about the Vietnam negotiations to Republican candidate Richard M. Nixon and offering secret anti-Nixon files to the camp of Democratic candidate Hubert H. Humphrey, according to a forthcoming account by investigative reporter Seymour M. Hersh.

Kissinger's role as a secret informant to the Nixon camp about the Paris peace talks, where he had been an unofficial consultant and confidential negotiator with North Vietnam on behalf of the Johnson administration, was disclosed previously in Nixon's memoirs.

In his book, "The Price of Power," to be published June 13 by Summit Books, Hersh also reports that Kissinger offered to help the Humphrey camp accumulate information to discredit Nixon, including private files that had been kept on Nixon by his Republican rival, New York Gov. Nelson A. Rockefeller. Kissinger, who had served for several years as Rockefeller's foreign policy adviser, was quoted by Hersh as offering to show the anti-Nixon documents to Humphrey's campaign adviser on foreign affairs, Zbigniew Brzezinski, if the arrangement were kept quiet and if Humphrey were told of Kissinger's help.

Hersh wrote that by the time the Democrats decided to accept Kissinger's offer Humphrey had fallen far behind Nixon in the public opinion polls and efforts to obtain the information were rebuffed by Kissinger's aides. But as Humphrey's poll ratings climbed shortly before the election, Hersh also reported, Kissinger wrote a letter to Humphrey criticizing Nixon and offering his services to a Humphrey administration.

By late September, 1968, according to Hersh, the Nixon camp had received its second report from Kissinger on the secret maneuverings at the Paris peace talks, and Kissinger was being informally slated to be White House adviser on national security if Nixon won the presidential race.

Meanwhile, in the Humphrey camp, a parallel process reportedly was under way. Hersh quotes Humphrey's confidant, Max Kampelman, as saying that Humphrey spoke of making Kissinger his White House adviser on national security if he won the election.

Neither Kissinger nor Nixon would comment yesterday on this or other aspects of Hersh's 698-page account, which has been long awaited by friends and foes of Kissinger and aficionados of the inner workings of foreign policy.

An aide to Kissinger, Chris Vick, said Kissinger has not seen the book and won't comment until he has.

An aide to Nixon, Nick Ruwe, said, "Former president Nixon only comments on his own books."

Hersh, who won a 1972 Pulitzer Prize for his account of the My Lai massacre and was a staff reporter for The New York Times from 1972 to 1979, said he spent 3 1/2 years reporting and writing his study of the Kissinger years.

Among the sources of his account, he said, were more than 1,000 interviews with American and foreign officials, a confidential diary kept by a White House staff member during the Kissinger era, secret papers on the Vietnam negotiations that had been provided to South Vietnamese President Nguyen Van Thieu by the Johnson administration and a host of other official and unofficial documents.

Despite many requests, neither Kissinger nor Nixon would consent to be interviewed for his book, Hersh said.

"Here's my interview with Henry Kissinger," said an enthusiastic Hersh, slapping down on his office table a dog-eared and battered copy of Kissinger's best-selling 1,521 page memoir, "White House Years," which covers the same period of time as does Hersh's volume.

While refusing to talk to Hersh, Kissinger communicated five times with Hersh's publisher through the law firm of Arnold & Porter to express concern in advance about the book and protest alleged inaccuracies in two Atlantic Monthly articles based on parts of the book.

A March 2, 1982, letter from attorney William D. Rogers, formerly Kissinger's undersecretary of state for economic affairs, sought to establish that Kissinger should not be treated as a public figure for the purpose of libel law, saying that the international celebrity "has been a private citizen, with the rights and protections of a private citizen, since January, 1977."

The Hersh volume describes duplicitous maneuvering within the White House and in the world of international diplomacy on a wide range of issues, including the Vietnam war and relations with the Soviet Union, China and other nations.

Among other things, Hersh wrote that:

* Morarji Desai, a veteran Indian political figure, was paid $20,000 yearly by the CIA during the Johnson administration and "undoubtedly" was the hitherto-unidentified confidential source who provided secret information from inside the Indian government during the 1971 Indian-Pakistan war. Desai later was Indian prime minister in 1977-79.

* A secret war plan commissioned by Kissinger and his senior military aide, Alexander M. Haig Jr., was completed in mid-1969 without the knowledge of Secretary of Defense Melvin R. Laird. The plan called for "massive bombing" of cities, harbors and dike systems in North Vietnam and destruction, "possibly with nuclear devices," of main north-south routes of the Ho Chi Minh trail.

* Stephen W. Linger, a code clerk in the Pentagon's highly secret communications center for "back channel" messages, relayed sensitive information to columnist Jack Anderson in 1971, causing "a panic" in the White House and Pentagon and touching off an investigation. A Navy stenographer in Kissinger's White House office, Yeoman Charles Radford, also provided Anderson with classified information and spied on Kissinger for the Joint Chiefs of Staff.

* Under pressure from Kissinger, the National Security Council and the CIA in 1972 inflated the numbers of ballistic missile submarines that the Soviet Union would be able to build in the years ahead, in order to make a Kissinger-struck deal on this issue in strategic arms limitation talks (SALT I) seem advantageous to the United States.

Hersh's book is a near-encyclopedic recitation of information about specific maneuvers, with little overall appraisal of Kissinger or his place in history.

Asked yesterday what he thinks of his subject after nearly four years of dogged study, Hersh replied, "I don't know him. But he's going to view this as a personal plot."