PARIS, NOV. 28 -- Prime Minister Jacques Chirac's government has won freedom for seven French hostages in its 20 months in power through a persistent combination of traditional diplomacy and off-the-books soundings in the shadowy underworld of Beirut kidnapers.

Like the Reagan administration, Chirac sought to renew a dialogue with Iran. Unlike the ill-fated U.S. effort, however, Chirac conducted his diplomatic approach with relative openness and made it clear to the French public as well as to Ayatollah Ruhollah Khomeini's envoys that he expected Iranian help on the hostages in exchange for improved relations.

Chirac, welcoming the two French hostages released yesterday, suggested today that the continuing French-Iranian discussions played a role in the latest liberation. After expressing joy at the return of journalist Jean-Louis Normandin, a 36-year-old television lighting engineer who was held 629 days, and Roger Auque, a 31-year-old free-lance reporter who was held 314 days, Chirac said:

"This liberation of two hostages . . . naturally makes us progress along the path of settlement of the disputes we have with Iran."

Chirac did not have to take the Reagan administration's secret route to Iran through Israel, because France had never insisted that it would have no contacts with Tehran. Instead of delegating contacts to a tight circle of aides with no Iranian experience, Chirac directed Foreign Minister Jean-Bernard Raimond to deal directly with the Iranian Foreign Ministry.

In addition to the overt contacts, Chirac's government has sought to open secret channels to the Beirut organizations holding French and other hostages, working through Iranian or Syrian officials. The release of Normandin and Auque appeared to be the fruit of such contacts, maintained directly out of Chirac's office and by aides to Interior Minister Charles Pasqua rather than through the Foreign Ministry or the Defense Ministry's intelligence agency, the General Directorate of External Security.

In another difference with the Reagan administration's approach, Chirac and Pasqua maintained detailed control over each step by their aides, according to descriptions provided today to the French news agency Agence France-Presse.

In an interview this week with the newspaper Le Figaro, Raimond said he and Chirac told Iranian officials from the outset that arms sales would not be part of the negotiations and that France would not abandon its support of, and arms supplies to, Iraq. Nevertheless, he said, these diplomatic contacts helped lead to the liberation of five French hostages between June 1986 and last December by Lebanese groups linked in one way or another to Iran.

The normalization with Iran was interrupted last summer after French security officials discovered apparent links between a Paris-based Iranian diplomat and Islamic fundamentalists accused of playing a role in terrorist bombings here. The diplomat, Wahid Gordji, has remained holed up in the Iranian Embassy here for six months to avoid responding to an investigating magistrate's summons.

But despite a formal break in relations and mutual recrimination, French officials said contacts with Iran continued. They were conducted regularly through Italy, representing French interests in Tehran, and Pakistan, representing Iranian interests in Paris, these officials said.

In addition, there have been news reports, denied by the government, that a French firm had shipped artillery ammunition to Iran until this summer, despite a government ban.

Three French hostages remain in the hands of Islamic Jihad, believed to be an operating arm of the Lebanese Hezbollah (Party of God) closely linked to Iran. Last night's release, however, was organized by the Revolutionary Justice Organization, a little-known group said by French experts to contain Iraqi Shiite Moslems and former members of disbanded Palestinian terror cells.

At the same time that Chirac pursued the contacts with Iran, he also maintained frequent diplomatic and security exchanges with Syria. French officials explained that the ties to Damascus were necessary because of President Hafez Assad's friendly relations with Iran and because the Syrian Army in principle controls large parts of eastern Lebanon and the Moslem sector of Beirut, where at least some hostages are believed to be held.

Raimond conveyed a message of thanks in a telephone conversation with his Syrian counterpart, Farouk Charaa, the Foreign Ministry announced today. Chirac, speaking at a welcoming ceremony for the two freed hostages this afternoon at Orly Airport, also referred indirectly to the Syrian role. He thanked "all the civilian and military authorities, French and foreign, for the help they gave us in the present circumstances and on the occasion of these last few days."

Le Monde said today that Chirac's government paid a ransom to obtain the release, suggesting that the French officials followed a channel opened when a West German businessman and a South Korean diplomat were freed recently after reportedly high ransom payments. Chirac categorically denied the Le Monde report.

The Revolutionary Justice Organization said it freed the hostages because it was assured by "friends" that "France will fulfill its promises in the near future."

Asked by reporters at Orly what France had pledged in return for the release, Pasqua declined comment.