For the past five years, the star of Saudi Arabia has been in swift ascendancy in Washington. Few governments today enjoy more favored-nation treatment from the Carter administration. And Saudis are becoming economic power brokers in U.S. board rooms.

The Saudis have the impression, as several have put it to us, that secret of Israeli political influence in the United States is Jewish financial power. There is reason to believe that the Saudis have deliberately sought to equalize this perceived Jewish financial pressure on U.S. policy-makers. "There's no question about it," one observer told us. "They want to manipulate policy by manipulating dollars."

Lewis Boden, the Treasury official in charge of Saudi Arabian affairs, disagrees. He told us that the Saudi government has a policy of never buying more than 4.5 percent of any company's stock and of keeping hands off sensitive industries like communications, transportation and energy. But individual Saudis, he acknowledged, have invested heavily in America at the grassroots. "I don't see how this might influence U.S. decision-making," said Boden, "unless you get businesses lobbying directly for the Saudis."

There is the celebrated example, however, of Saudi entrepreneur Ghaith R. Pharaon. Armed with a fat checkbook, he has become a banking partner not only of President Carter's close crony, Bert Lance, but also of Republican presidential aspirant John Connally. Both know how to pull strings in Washington.

We have also established that Ghaith Pharoan is the son of King Khalid's trusted political adviser, Rashad Pharaon. Saudi sources have conceded that the son doesn't make a move without checking with his father.

The bank ventures that put Pharaon in business with Lance and Connally are merely the Arabian camel's nose under the U.S. economic tent. "It's just the most recent visible activity." a congressional source told us. "The Saudis have immeasurable but constantly growing economic clout in American banks. Such economic power translates into an immediate growth of political influence."

As part of our investigation into the buying of America by foreign interest, we have spent several months pursuing Saudi financial investments. No firm figure can be obtained on how much the Saudi have plunged into this country. A spokesman at the Treasury refused to give out any information lest the Saudis be offended. "It's their money, and we know they're sensitive about it," he said. Sources close to Treasury Secretary W. Michael Blumenthal, however, say he has placed the Saudi holdings at $50 billion to $70 billion. Through government files and financial circles, we have tracked down some typical Saudi investments:

The Saudis are said to be the largest single holder of Federal Home Loan Mortgage Corporation bonds. The money from these "Fanny Mae" bonds is funneled by banks into millions of home mortgages. We've learned that the chief finance officer, Robert Bennett, has traveled to Riyadh, the Saudi capital, to hawk more of the bonds.

The Saudis have quietly granted "private placement" loans worth $300 million to American Telephone and Telegraph and three of its operating companies - Northwestern Bell, Pacific Bell and Southwestern Bell. At least two other corporate giants, U.S. Steel, and Pacific Gas and Electric, have obtained multimillion-dollar private placements from the Saudis. They have been made through four main U.S. investment bankers - White and Weld, First Boston Crop., Morgan Stanley and Salomon Brothers.

The Triad Holding Corporation, an international holding company with headquarters in Luxembourg, is controlled by Saudi financier Adnan Khashohhi. In 1974, Triad bought a 15 percent interest in the Arizona-Colorado Land and Cattle Company. The $9.4 million payout gave Khashoggi control of 155,000 acres of land in Southwest Colorado. Another $10 million of Khashoggi's money was plowed into a industrial park in Salt Lake City. He sold his interest a few months later for a quick turnover.

Ghaith Pharaon last year grabbed up 32,600 acres of Louisiana timberland between New Orleans and Baton Rouge. The $10 million deal was swung by the Arabian Services Corporation, a Houston company that fronts for Pharaon. Exploration has begun on the Arabian-owned tract for oil and gas.

The Saudis are just beginning to invest their petro-profits in U.S. real estate, our sources say. Most of their property purchases center around Houston, because it's the home of the major oil companies. But Saudis have also been buying up mansions and other fashionable residential properties in the San Francisco area.

But if some congressmen fear the Saudis are investing too heavily in America, others are worried that the Saudis will take their petrodollars elsewhere. The Securities and Exchange Commission disturbed over Saudi financial manipulations, has been investigation Khashoggi with a vengeance. That was the real he pulled out of his Salk Lake City investment and is now pouring his millions into European, enterprises, an attorney for Khashoggi told us.

The sheer magnitude of the petroldollar accounts can tilt the economy. In 1976, for instance, the oil states deposited $1.6 billion in U.S. banks, only $500 million in foreign banks. An estimated 80 percent of that was Saudi money. But there was a decline of confidence in the United States. So 1977 brought a dramatic reversal: $2.5 billion in petrodollars was deposited in bank accounts outsidethe United States, only $400 million in U.S. banks.