BEIRUT, Lebanon (AP) _ Three Soviet-made missiles slammed into the gardens around President Amin Gemayel's palace today, causing damage but no casualties, authorities said.

Police said the 9-foot-long Grad missiles were fired from Syrian-policed Moslem west Beirut, but it was not clear who launched the attack on the hilltop palace in the Christian suburb of Baabda.

It came after Moslem leaders blamed Christians for the June 1 assassination of Prime Minister Rashid Karami, a Sunni Moslem.

Acting Prime Minister Salim Hoss arrived in Damascus today for talks with Syrian Vice President Abdul-Halim Khaddam on the political situation after the assassination.

Hoss, accompanied by Parliament Speaker Hussein Husseini, was greeted in Damascus by Deputy Prime Minister Salim Yassine.

Several of the principal powerbrokers in Lebanon have also traveled to Damascus this week for talks, among them Druse warlord Walid Jumblatt, Nabih Berri, leader of the Shiite Moslem Amal militia, and George Hawi, head of the Moscow-oriented Lebanese Communist Party.

Jumblatt commented: ''The situation in Lebanon is being completely reconsidered in light of the Karami assassination.''

He did not elaborate. But Moslem and leftist militias have accused Israel and the right-wing Lebanese Forces, the Christians' main militia, of murdering the pro-Syrian Karami in collaboration with Christian army officers.

The Lebanese Forces and the army have denied the allegations.

Karami died when a bomb exploded aboard a military helicopter that was to take him from north Lebanon to Beirut.

Gemayel, a Maronite Catholic, told senior U.S. and Soviet diplomats Tuesday that he would push for the ''maximum penalty'' for Karami's assassins, a palace source said.

The source, who spoke on condition of anonymity, said Gemayel also briefed the British, French and Chinese ambassadors on the ''threats facing the nation'' following Karami's assassination.

There are mounting differences between Christian and Moslem leaders about how to investigate Karami's slaying, which threatens to touch off a new round of sectarian violence in Lebanon's 12-year-old civil war.

Syria is the main power broker in Lebanon. It maintains 25,000 troops in east and north Lebanon under a 1976 Arab League peacekeeping mandate.

Syria also deployed 7,500 troops in west Beirut Feb. 22 to quell militia clashes in which 300 people were killed.

Army, parliamentary and judicial teams are carrying out separate investigations to determine who killed Karami.