Rep. Jack Kemp (R-N.Y.) no longer feels bound to honor his commitment to support Ronald Reagan for president in 1980 and may announce his own candidacy in November, disturbing Reagan's majestic march toward the Republican nomination.

Kemp's private pledge of support three months ago has been regarded within the Reagan camp as a bulwark of its campaign for maximum support within the party's dominant conservative wing. But that was always considered a blunder by Kemp advisers, and the congressman himself felt relieved of the promise when the Reaganites publicly revealed it.

Thus, as Kemp ponders conflicting advice whether to make an announcement in November, he is not inhibited by ties to Reagan. Whatever he does in November, after the midterm election, chances are better than even he will run for president in 1980. With conservative Rep. Philip Crane of Illinois the first announced candidate and with Kemp himself the hottest current attraction on the Repulican banquet circuit, Reagan's hopes of monopolizing the Republican right are being shattered.

Kemp's presidential thoughts actually go back to last January when he dined in Manhattan with close advisers (including writer Irving Kristol and Jude Wanniski, then a Wall Street Journal editor). It was decided that instead of running for governor of New York this year, Kemp should wait for two 1980 options: a run for the Senate seat now held by liberal Republican Jacob Javits - or the presidency.

Nevertheless, Kemp was unprepared for the May 6 syndicated column of conservative James J. Kilpatrick, pushing Kemp for president and writing off Reagan as "getting a little long in the tooth." That was too much, too soon for Kemp, who entered politics as an off-season aide for then - California governor Reagan while still playing professional football.

Shortly after Kilpatrick's column, Reagan aide Peter Hannaford telephoned Kemp for an appointment. Before Hannaford could say anything in the meeting at the congressman's office, Kemp volunteered this: Forget the Kemp-for-president talk; count me in supporting Reagan if he runs; I'll be trying for the Senate, whether or not Javits quits.

Kemp's inner circle was horrified. He defended his action on grounds that Reagan was the only prominent Republican then praising Kemp and the Kemp-Roth tax-reduction bill, and also was stressing national defense, Kemp's other big issue. Besides, with Crane's candidacy not yet surfaced. Reagan seemed to have the conservatives to himself.

But a small cloud appeared. After meeting Hannaford, Kemp called Reagan in California, pleading with him to help ex-Reagan aide Feffrey Bell's seemingly quixotic effort to unseat liberal Sen. Clifford Case in the New Jersey primary. Could Reagan at least raise money for Bell? Reagan, seeking to prove himself no right-wing party-wrekcer, declined.

On May 12, Kemp adviser Wanniski, in California on a last assignment for The Wall Street Journal before resigning from the paper, lunched in Los Angeles with Reagan aide Hannaford. Wanniski's message: You can't hold Kemp to support Reagan.

Wannaski argued that Reagan broke the compact by rejecting Kemp's plea to help Bell. But anyway, he continued, this was force majeure - an irresistible power; the tide building behind Kemp would sweep away trivial personal promises.

Kemp's self-described "bomb thrower>" Wanniski, was not authorized by the congressman to make those arguments. Kemp does not discount the force majeure theory, but he has never agreed that Reagan's non-support for Bell (who won in New Jersey anyway) invalidated his commitment to Reagan.

However, a reason for disconnecting from Reagan was supplied by our column of June 4, which reported Kemp's pledge. George Bush, himself a presidential hopeful, telephoned Kemp in alarm. So did businessman Leon Parma, an intimate of Gerald Ford.

Kemp then called hannaford, saying how unhappy he was to see their "private" conversion in print. Although he did not specifically so inform Hannaford, Kemp believes that was a breach of confidence relieving him of his commitment.

Since then, the Republican National Committee has adopted the Kemp-Roth bill as party doctrine, and Kemp has attracted a spectrum of boosters of all ideological colors seeking a new face. Irving Kristol wants Kemp to announce in November and urge all other aspirants also to get in - precisely what Reagan does not want. In Kemp's office, Kristol's suggestion has been subject to intense debate.

But November is not the point of no return. When Kemp attended Football Commissioner Peter Rozelle's annual party at his Westchester County estate Aug. 11 corporate magnates were enthusiastically talking Kemp for president. That is moving toward the "critical mass" that Wanniski feels makes Kemp's candidacy unavoidable. Certainly, no commitment to Reagan will no obstruct it.