San Marino's new honorary consul in Washington comes to the job with some interesting connections. She is the daughter of the U.S. ambassador to Italy, and her selection was made by the fabulously wealthy Baron Enrico di Portanova, whose wife is on the 29-member White House Preservation Fund board of trustees. That membership now requires a $250,000 contribution.

The situation involving Sheila Rabb Weidenfeld, her father, Ambassador Maxwell Rabb, and di Portanova, who in his nonpaying job of San Marino's consul general is Weidenfeld's boss, may pose some tricky questions for the Reagan administration.

San Marino has had a history of on-again, off-again communist governments since the end of World War I. Besides getting much of its oil from the Soviet Union, San Marino's communist ties reach right into its own government, a coalition of the communist and socialist parties that came to power in the 1978 elections. San Marino is the world's oldest and smallest republic and is nestled on a mountaintop, surrounded by Italy.

In March, its parliament voted to "deplore" U.S. government action in El Salvador and authorized a symbolic contribution of 5 million lira (about $4,050) to El Salvadoran rebels after two rebel representatives met with Sanmarinese Foreign Minister Giordano Bruno Reffi.

"Rabb has to represent the policy of the United States in Italy, so how is his daughter going to represent a contradiction of that policy. . . .?" asks Baron Pier Arrigo Breschi, a wealthy Sanmarinese businessman with offices in New York and Italy and a vocal member of the Christian Democratic party, which opposes the current government.

Weidenfeld, former press secretary to former first lady Betty Ford, shrugs off the notion that she might present a conflict of interest to her father in her representational tasks, which include promoting friendly relations with the United States.

"It's a democracy in the real sense. You never know who's in power," says Weidenfeld, a U.S. citizen, about San Marino. "The only concern was El Salvador and we had a good talk with Reffi--look, what am I going to say in the most diplomatic way? He understood."

And what of the Soviet oil?

"Gee, I've really got to brush up on all that," says Weidenfeld.

The State Department didn't shrug off the possibility of a conflict of interest, at least at the outset, and according to one State Department official, it sought a ruling from its legal department.

"There was a consideration here as to whether it would be a conflict, but from the ambassador's point of view the conclusion was reached that there was none," said the official. "After due consideration, it was agreed that we would accept her. She's a private person, and if she is acceptable to San Marino, there is no reason we should not recognize her."

Associate chief of protocol Richard Gookin, however, describes San Marino's request for recognition of Weidenfeld's appointment by the State Department as "routine--it contained no information that led us to think otherwise."

Weidenfeld says she consulted her father shortly after she was offered the post by the increasingly more visible Baron di Portanova, and Rabb didn't object.

As a matter of fact, she says he thought it would be "fun." She says the position provides no paycheck, only a diplomatic passport. The State Department, however, says Americans serving in honorary consul capacity do not travel on diplomatic passports.

Rabb was among guests who attended di Portanova's installation as honorary consul general in San Marino last fall. The ambassador's presence raised a few Sanmarinese eyebrows, since relations between San Marino and the United States are on the consular rather than ambassadorial level.

In New York early last month, the di Portanovas gave a party for Weidenfeld and her husband Ed, and the guest list included the Rabbs, Rep. John LeBoutillier (R-N.Y.), Buffy and William Cafritz, deputy assistant to the president and director of presidential personnel Helene von Damm and the Italian Ambassador Rinaldo Petrignani.

Di Portanova's vast wealth comes from Texas oil on his late mother's side. Texas Monthly, in its March 1982 issue, raises some questions about di Portanova's nobility, but in this country he and his wife have already established their access to power. The magazine estimates his net worth at about $50 million and his annual income at $8 million. In San Marino, there are unconfirmed reports that di Portanova has contributed several million dollars to build an airport.