Shortly after 11 a.m. yesterday, as the House was beginning final debate on aid to the rebels in Nicaragua, Rep. James R. Jones (D-Okla.) was back in the cloakroom, on the line with the president of the United States.

First, he had to get something off his chest. Jones said he told President Reagan that he decried the "McCarthy-like tactics" used to impugn the character of some of his colleagues who opposed the plan, and said it almost cost the White House his vote.

Reagan disowned the attacks and then made two promises to the seven-term congressman and unannounced candidate for the Senate.

Reagan assured Jones that he would not send U.S. troops to Nicaragua, as House Speaker Thomas P. (Tip) O'Neill Jr. (D-Mass.) and others predicted would happen eventually if Congress approved the $100 million package.

"He said it would not be supported by American public opinion and we would lose all our friends in Central America," Jones recalled.

Reagan also agreed to invite leaders of the four-nation Contadora group to the White House "or find a similar way to show our full support for a diplomatic effort for regional peace." Jones said that persuaded him the White House "hard-liners" itching for a fight would not control administration policy.

After weeks of indecision, Jim Jones had his ticket and was ready to climb aboard. "I'm one telephone call away from voting yes," Jones said as he stepped briskly across the Capitol grounds toward his office. Last year, the Oklahoman had opposed military aid to the contras but supported nonlethal assistance.

Jones never connected on that final call, to Adm. William J. Crowe Jr., chairman of the Joint Chiefs of Staff, even though he kept trying up to the final speech of the debate. Crowe was traveling. But it didn't matter. By the time the roll was called at precisely 2:30 p.m., the White House had Jones, one of 32 moderate Democrats whose swing votes were considered crucial to the outcome, on its side -- albeit the losing side.

En route to his decision, Jones traveled a well-worn path that often detoured from the fierce rhetoric, emotional floor speeches and backroom horse-trading considered so much a part of Washington lore.

There were phone calls and private meetings with career diplomats and military officers Jones respected, who presented a calmer view of the administration's intentions than the often strident rhetoric coming out of the White House.

Jones also was persuaded by Reagan's pledge on Wednesday to issue an executive order that would restrict the use of the money for 90 days while diplomatic efforts continued. Many of his colleagues didn't buy the offer, but Jones, a former top aide to President Lyndon B. Johnson, did.

"I will admit that the use of letters has created a jaded attitude around Capitol Hill because they have been used on different occasions and they haven't been fully fulfilled," Jones said. "I still have deep respect for the office of the presidency -- having worked there for four years myself."

Back home, where the economy has been battered by falling oil prices and bankruptcy among farmers, newspaper ads and radio spots were stirring up emotions, with mail and telephone calls to Jones' Tulsa office running 2 to 1 in favor of the president's plan. That too helped tip the scale on the White House's side for Jones.

Finally, Jones, a moderate Democrat, was staring straight at a challenge to Sen. Don Nickles (R-Okla.), a well-funded Reagan conservative in a state where many voters are "hawks in their own head," according to Lawton, Okla., Mayor Douglas Gilley (D).

Jones, who said he always has felt that "good policy is good politics," insisted that the vote on contra aid would be insignificant in the Senate race. In the end, he acted in a way that may assure that it isn't an issue. Tom Cole, the state GOP chairman, who wasn't asked, said he would have advised Jones to "go along with Reagan."

From the beginning, Jones disliked the all-or-nothing terms of the vote. He portrayed himself as a policy-oriented pragmatist "caught in the power play" between "the hard-liners in the White House and the hard-liners in Congress."

An unbridled military approach would merely "repeat the banana republic mistakes" of earlier years, he said. "If nothing is the alternative, that is not the policy either."

Jones preferred the approach of his colleague, Rep. Dave McCurdy (D-Okla.), who wanted to emphasize a regional peace effort and tie the use of military funds to aggressive pursuit of such a policy.

Moreover, he feared a GOP ploy. "One thing that troubles me with the excessive rhetoric that's come out of the White House," Jones said last week, "is that they may look at the intelligence information and conclude that the contras can't win even with $100 million, and they're setting up a political fall guy -- namely the Democrats or Congress in general."

At the time he was fuming over the tactics of some of the proponents, who had introduced "a mean-spiritedness and a know-nothingness to the process."

In the middle of the week, Richard L. Armitage, assistant secretary of defense for international security affairs, called to check Jones' temperature. "I told him my temperature was at the boiling point," Jones said.

Before he left Washington for a long weekend back home in Tulsa, however, Jones talked for about an hour in his Capitol Hill office with Gen. John Galvin, commander of the U.S. forces in Central and South America.

Galvin told Jones that the contras were a "fairly significant force." They could win with time and the right support on their side. The conversation with Galvin moved Jones off dead center as he headed home.

While Jones had been mulling over his decision in Washington, things had begun to stir in Oklahoma.

Jeane J. Kirkpatrick, former U.S. ambassador to the United Nations, addressed a joint session of the state legislature, appealing for support for the president's plan. A conservative group, meanwhile, had begun to air radio ads, one of which included excerpts from President Reagan's statements in support of contra aid, punctuated this way:

"President Reagan's exactly right . . . but your congressman, Jim Jones, doesn't see the consequences of having a communist regime only two days' driving time from Texas . . . . For America's sake, call Congressman Jones right now . . . . "

It was at home in Tulsa that Jones said he almost decided to vote no just to spite the right-wingers. But his wife Olivia would have nothing of it.

"She was the one who said, 'If you let them run your life you're as low-level as they are.' She was the one who got me back on track," Jones said.

Back in Washington, Jones called Philip C. Habib, the career diplomat who Reagan had hastily appointed as a symbol of his willingness to pursue diplomatic alternatives to a military plan, for an off-the-record assessment.

Habib assured him, Jones said, that the governments of other Central American nations felt "a military presence has to be kept in order to realize negotiations."

Habib also assured Jones in the telephone conversation that he himself was not -- and would not -- become an empty White House pawn who would never pursue a diplomatic solution.

Reagan's announcement on the eve of the vote that he would issue the executive order if the measure passed took Jones "95 percent of the way" toward the approach he always had preferred, and the 20-minute conversation yesterday with Reagan completed the journey.

At 2:46 p.m., applause broke out in the House chamber as Jones was being interviewed in the lobby outside. He walked in, glanced up at the electronic vote counter and learned that neither he nor Reagan had prevailed.

His Democratic colleagues were smiling and applauding. Jim Jones did not join in.