Conventional -- or nonnuclear -- forces of the North Atlantic Treaty Organization (NATO) are not substantially weaker than the conventional forces deployed by the Warsaw Pact, according to a study released yesterday by Sen. Carl M. Levin (D-Mich.), chairman of the Armed Services subcommittee on conventional forces.

"I believe an uneasy conventional military balance exists today in Europe," Levin told reporters after what he described as an extensive review of committee testimony, intelligence briefings, and reports by independent experts and the Joint Chiefs of Staff.

Aides said the release of Levin's 67-page report was timed to influence congressional debate on the military implications of the U.S.-Soviet treaty on Intermediate-Range Nuclear Forces (INF), which the Reagan administration will formally submit for Senate approval next Monday.

Conservative critics of the INF pact, such as former NATO military commander Bernard W. Rogers, have charged that its proposed elimination of U.S. and Soviet medium- and shorter-range nuclear missiles would leave U.S. allies in Europe vulnerable to the threat of attack from superior Soviet conventional forces.

Sen. Jesse Helms (R-N.C.), who pledged yesterday to try to amend the INF Treaty -- effectively killing it -- complained that "with the removal of intermediate-range nuclear missiles, we would have to be willing to spend billions -- billions we don't have -- for {a} major expansion in conventional forces."

But Levin challenged what he called the traditional "bean-counting" approach to the East-West conventional balance in Europe, in which the Warsaw Pact is judged superior because it has more weapons than NATO.

"The balance . . . is far more complex than usually portrayed by both Western government officials and the news media . . . involving much more than the sheer size of the military forces that wage {war}," Levin said.

He said the United States could enhance its security by negotiating a withdrawal of Warsaw Pact armed forces.

In addition to comparing numbers of weapons, Levin and staff aide Greg Weaver calculated the relative quality of NATO and Warsaw Pact forces, their readiness for war, ability to fight over a long period, loyalty and other factors.

Levin concluded that the Warsaw Pact forces were superior in six categories, including positioning of forces, ability to function under a single command, and to mobilize quickly for war. But he concluded that NATO was superior in five categories, and roughly equal in two.

The International Institute for Strategic Studies, based in London, reached similar conclusions late last year.

"NATO has considerable strengths, and is by no means a basket case in terms of conventional military power versus the Warsaw Pact," Levin's report stated.

The report noted that while a typical calculation reveals 52,200 Warsaw Pact tanks to NATO's 22,200, this "conceals the fact that 56.9 percent of the Pact tanks are models designed before 1965," while only 19.1 percent of NATO's tanks are of similar age.

Moreover, in the central region of Europe, which is thought likely to be the initial East-West battleground in the event of a conflict, the Warsaw Pact has 18,000 tanks compared with NATO's 12,700, Levin said. Other analysts have suggested that the superiority of U.S. antitank weapons further reduces the difference.

Levin concluded that NATO may need major improvements in communications systems and ammunition stocks to ensure that it can adequately defend against a Warsaw Pact attack. It also needs to supply more standardized weapons to troops from different countries to help avoid confusion on the battlefield.

But he added that if NATO believes it is "hopelessly outmatched in conventional strength, we could make ourselves the victims of a self-fulfilling prophecy of conventional military inferiority or political blackmail."