WASHINGTON (AP) _ The harassment of a Jewish dissident invited to dine tonight with Secretary of State George P. Shultz in Moscow belies Soviet claims of a new openness, former United Nations ambassador Jeane J. Kirkpatrick says.

''What it means is nothing has changed as much as we all wish it would,'' Kirkpatrick said after a Sunday rally on the Capitol steps for Vladimir and Maria Slepak.

She was joined by Nobel Peace Prize winner Elie Wiesel and the Slepaks' sons, Alexander and Leonid. Alexander, a 35-year-old medical student at Temple University in Philadelphia, finished a 17-day fast Sunday, as did his father in Moscow, marking the end of the 17th year since the elder Slepaks first were denied permission to emigrate.

Vladimir and Maria Slepak have been staging silent protests in front of the Russian Federation Building. But they were seized Saturday by uniformed militiamen, shoved inside a jeep, driven home and told not to demonstrate again.

''I think its shocking,'' said Kirkpatrick, U.N. ambassador during President Reagan's first term. ''What harm does this one man - Vladimir Slepak seeks only to control his own life in a very private way - do to ... this enormous powerful state?''

''I have personally no doubt that George Shultz will take it very seriously indeed,'' she said.

Shultz arrives in Moscow today for three days of official meetings with Soviet leader Mikhail S. Gorbachev and Foreign Minister Eduard A. Shevardnadze. The secretary's jet carries kosher wine and matzo, the unleavened bread eaten at Passover to mark the Jews' wanderings during the exodus from Egyptian slavery.

Tonight, Shultz is to take part in a Passover Seder at the American ambassador's residence with the Slepaks and other prominent refuseniks - Jews who have been refused permission to emigrate.

Wiesel, a Holocaust survivor and writer, making his remarks in the form of an entreaty to Gorbachev, said: ''Let them leave. It's enough. Seventeen years is enough. Why do you keep them there? Is it because they were ... among the first to start the (emigration) movement and therefore you choose ... they should be the last?''

Then, to Shultz, he said: ''I hope that in Moscow as you meet Soviet leaders, you will do everything, literally everything, to see the Slepaks.''

Alexander Slepak said his parents were told Saturday that they could not leave their apartment building, but the elder Slepak said in a telephone interview Sunday that a guard remained outside his home for only a few hours. He said he plans to attend the dinner with Shultz.

Slepak, now a Hebrew teacher, has been told his visa has been denied because of his work with state secrets as an electronics engineer between 1957 and 1969. But his supporters say his work has long been out of date.

Noting Gorbachev's push for democratization, Alexander Slepak said, ''I want (Soviet authorities) to show that while they're talking about freedom and possible changes, we want the deeds and not the rhetoric. ... My parents are 60 years old. When they applied, they were 43. That's cruelty; that's not change.''