Frank Sinatra has filed a $22 million suit against the National Enquirer about an article in the supermarket tabloid that said he went to a clinic in Switzerland for injections of youth serum made from sheep cells. Sinatra had unsuccessfully demanded a retraction . . .

While Capitol Hill was swarming with supporters of federal credit aid for failing farmers, Senate Majority Leader Robert J. Dole was worried about getting out in time for dinner. Monday, he told some reporters in the well of the Senate, just before opening the business of the day, that there wouldn't be any late roll-call votes because he had a reservation for dinner at the expensive French restaurant Lion d'Or . . .

Scott Cohen, who spent 20 years as a top aide to former senator Charles Percy going back to Percy's unsuccessful bid for the governorship of Illinois in 1964, is leaving the Senate Foreign Relations Committee, where he had been Percy's staff director before the senator's defeat in November. There will be a going away party for him in the Foreign Relations Committee room tonight with a guest list that is to include former United Nations ambassador Donald M. McHenry; Peter McPherson, director of the U.S. Agency for International Development; former U.S. Ambassador to Egypt Roy Atherton and former Iranian hostage L. Bruce Laingen . .

Reelection time is coming and Sen. Bob Packwood is courting Jewish voters. He has sent out thousands of fund-raising letters across the country, each containing an Israeli shekel. His press secretary Etta Fielek says Packwood has carried one of the Israeli coins in his pocket for years from a trip he took to Israel and as a symbol of his commitment. He'll need more than shekels for his 1986 reelection campaign, since a shekel is worth only about a tenth of a cent . . .

For what it's worth, NCPAC chairman Terry Dolan has conducted his own "Ann Landers sexual survey" to see if "cuddling" is preferable to "the sex act." After surveying 1,010 people (503 men and 507 women), the results are cuddlers, 36 percent; the act, 29 percent; and those who didn't know or were not about to tell him, 35 percent . . .

Washington reporters gave Vice President George Bush another opportunity to take a kick at former opponent Geraldine Ferraro at a National Press Club appearance this week when he was asked if he had lost, would he make a Diet Pepsi commercial as Ferraro is doing. After a pause, he gave a Texas answer: "If a frog had wings, he wouldn't hit his tail on the ground" . . .