BANGKOK, Thailand, Jan. 23--President Sukarno of Indonesia has thrown a monkey wrench into mediation machinery built up by U. S. Atty. Gen. Robert F. Kennedy for a settlement of the Malaysian crisis.

Sukarno vowed continued hostility toward Malaysia in a speech in Jakarta tonight, right after Kennedy left for Washington with an agreement among Indonesia, Malaysia and the Philippines on steps toward peace.

The mercurial Indonesian leader told a rally of 15,000 cheering youths that his island nation will press its drive to crush Malaysia unless that anti-Communist federation of former British colonies is changed to suit Indonesian tastes.

"Onward, never retreat!" Sukarno said. "Crush Malaysia! Indonesia may change its tactics, but our goal will remain the same."

Before he left Bangkok on a nonstop flight to London, and before he knew of Sukarno's latest declaration, Kennedy had said:

"I am confident that the Asian countries concerned will find a peaceful solution to the differences that now separate them."

Tax Cut Gains

WASHINGTON, Jan. 23--The Senate Finance Committee gave final approval today to an $1.5 billion tax-cut measure, keeping alive administration hopes for Senate passage by Feb. 11.

The committee in a 12-5 vote finished its reshaping of the House-passed measure which President Johnson is counting on to forestall-any threat of a business downturn in this election year.

The bill came out of the Finance Committee in roughly the form asked first by President John F. Kennedy and then by Johnson. The President's supporters in a last-minute rally won a reversal of a series of surprise votes to lift man-excise taxes--at an estimated revenue loss of $455 million, compared with 1963.

Castro Backs Soviets

MOSCOW, Jan. 23--Fidel Castro apparently has committed himself at last on Premier Krushchev's side in the Moscow-Peking feud after he was promised a better deal for Cuban sugar.

The Cuban prime minister flew back to Havana today after voicing support for the nuclear test ban treaty.