President Reagan yesterday sent Congress a controversial, long-awaited report charging that the Soviet Union over the past 25 years has broken half its arms control agreements with the United States through "violations, probable violations, or circumventions."

A 17-page unclassified summary of the 300-page secret report, prepared by a civilian advisory committee on arms control, concludes that the Soviet actions "demonstrate a pattern of pursuing military advantage through selective disregard" for its agreements.

The president, who was pressured to release the 10-month-old report by conservative Republicans in Congress, distanced himself from its findings by saying, in an accompanying letter, that "neither the methodology of analysis nor the conclusions reached . . . have been formally reviewed or approved by any agencies of the U.S. government."

The Reagan administration has been split for months over releasing the report by the General Advisory Committee on Arms Control and Disarmament. State Department officials have sought to keep it secret, fearing its unproved allegations and tough conclusions would arouse Moscow and further aggravate U.S.-Soviet relations.

Pentagon officials, on the other hand, have supported release of the report, arguing that it proved the need for tight verification provisions in any agreement with the Soviet Union.

One of the report's conclusions is that the "committee found recurring instances of Soviet conduct involving deliberate deception, misdirection and falsification of data during negotiations."

Last month, the release was delayed because of Reagan's talks in Washington with Soviet Foreign Minister Andrei A. Gromyko. At that time, White House aides promised legislators that the document would be sent to Capitol Hill before Congress adjourned.

The report describes 17 incidents going back to 1961, and concludes that they represent nine violations of agreements, two probable violations, four breaches of commitments and two circumventions of agreements.

The report also reviewed 15 "areas of Soviet activity that raise suspicion of further material breaches of arms control agreements."

Most of the recent incidents described in the unclassified summary and bearing on strategic arms agreements were contained in the president's own list of nine alleged "Soviet violations or probable violations," which was sent to Congress last January.

Other incidents, which some administration officials describe as less important, focus on older events such as venting in underground atomic tests that the report says violates the 1963 partial test ban; transiting the Turkish Straits with aircraft carriers, which violates the 1936 Montreux Convention, and using booby-trap mines and incendiary weapons against civilians in Afghanistan, which it describes as violating a 1981 conventional weapons convention.

The committee and the president apparently disagree on the best way to bring about Soviet compliance with agreements.

In his letter yesterday, Reagan said the administration is "actively pursuing" compliance "in confidential discussions with the Soviet Union."

The committee, on the other hand, charged that "near total reliance on secret diplomacy in seeking to restore Soviet compliance has been largely ineffective."

Instead, it calls upon the administration to develop a strategy "to deter and if necessary initiate measures to offset Soviet arms control noncompliance." One method, it suggests, would be to make public instances of noncompliance such as was done with Soviet use of chemical and toxic weapons in Afghanistan. That act, the report says, "may have contributed to limiting the extent of these prohibited activities."