ALMA-ATA, Kazakhstan — Bearing promises of aid and a visit with Bill Clinton, Secretary of State Warren Christopher won a pledge from Kazakhstan's president Sunday to secure ratification of the Nuclear Non-Proliferation Treaty by the end of the year.

The move means that Kazakhstan is likely to renounce nuclear weaponry once Soviet-era missiles and bombers are removed from its territory.

But Christopher faces a tougher test today: a meeting with the president of Ukraine, who has suggested that he wants to cut a separate deal over some of the roughly 1,800 nuclear warheads his country inherited from the Soviet Union.

The Kazakh president, Nursultan Nazarbayev, surprised U.S. officials with the pledge, which he offered in exchange for a promise of a meeting with President Clinton, probably early next year.

In addition, Christopher announced a package of up to $140 million in aid for Kazakhstan for the new fiscal year that began this month, about triple the amount offered last year.

Aides to Christopher said Nazarbayev's action is important for two reasons: It is the first time the Kazakh leader has publicly promised to join the treaty by a specific date, and it will help the secretary of state put more pressure on Ukraine to dismantle its missiles.

Ukraine's arms stocks put it behind only the United States and Russia as a nuclear power. Ukrainian President Leonid Kravchuk has repeatedly promised to dismantle the arsenal, only to delay the pledge in the face of demands from nationalist groups.

Christopher flew to Kiev, the Ukrainian capital, Sunday night to urge Kravchuk to give up the nuclear weapons, but an aide said: "We are not very optimistic."

Kravchuk told reporters in Kiev last week that he does not believe the existing agreements on nuclear weapons require him to destroy all of Ukraine's missiles.

U.S. officials were dismayed by the statement.

The Administration is concerned that Ukraine's government is gradually taking over command and control of the nuclear weapons on its territory, supplanting Russia's role, a senior U.S. official said.

Christopher is visiting all four countries that inherited Soviet nuclear weapons--Russia, Ukraine, Kazakhstan and Belarus--with the aim of keeping their disarmament plans on track.

Ukraine, Kazakhstan and Belarus promised last year to either dismantle their nuclear weapons or ship them to Russia for dismantling there, but so far only Belarus has taken significant steps toward disarmament.