TEL AVIV, Israel (AP) _ Israel and the United States signed an accord giving Israel about $6 million to research strategic missile defense systems as part of President Reagan's ''Star Wars'' program, a Defense Ministry spokesman said today.

Israel in May became the first non-NATO country to join the research program into space-based defense, officially called the Strategic Defense Initiative.

Israel is expected to research a defense against Soviet-made SS-21 medium- range surface-to-surface missiles which were recently deployed in Syria, a defense industry source told The Associated Press.

The Israel Arms Development Authority - called Rafael - and Israel Aircraft Industries are expected to be main beneficiaries of the grant. The two companies jointly developed the Barak shipboard point-defense anti-missile missile, said the official, who asked not to be identified by name.

The agreement was signed Wednesday by Defense Ministry Director General David Ivry and Deputy Director of SDI research, Gordon Smith, said spokesman Dan Weinreich.

Defense Ministry sources expressed disappointment over the size of the grant, the Jerusalem Post reported today. The United States has budgeted $26 billion for SDI research.