If the Secret Service were given twice as much money as it gets now to protect the president, how would it use the extra funds?

Secret Service Director H. Stuart Knight was asked that question, a tantalizing one for any federal manager, at an appropriations hearing on Capitol Hill last week. After a long, thoughtful silence, he said, "My response would be, in some way, to try to enhance our intelligence capability." r

It is doubtful that the Secret Service's $178 million annual budget will be doubled, as Rep. Clarence Miller (R-Ohio) hypothesized when he asked Knight that question, but it does seem likely that Congress -- in its zeal to do something in response to the March 30 shooting of President Reagan -- will do what it can to help Knight increase his agents' ability to gather information about individuals and groups the service thinks might pose a threat to the president.

Congress has reacted to the assassination attempt with a flurry of legislation and a flood of suggestions for the president and his protectors. The ideas range from the call by Sen. Edward M. Kennedy (D-Mass.) for a new effort at gun-control legislation to the recommendation by Sen. Larry Pressler (R-S.D.) that Reagan wear a military flak jacket whenever he goes outside ("I know these jackets are bulky," Pressler wrote the president, "but it is essential we take all steps to protect . . .")

But gun control seems doomed, as usual, to be lobbied to death, and it is likely that the only legislation in the whole crop of post-shooting bills that will become law is a measure toughening penalties for anyone who shoots the president. The experts say it is doubtful that the deranged people who tend to shoot at presidents would be deterred by the threat of penalty. The man charged with shooting Reagan, John W. Hinckley Jr., wrote beforehand that he almost expected to die in his assassination attempt -- but he went ahead.

And so Congress and the executive branch have focused on domestic intelligence as something where changes can be made.

Here, too, it should be noted, nobody suggests that sharpened surveillance of those deemed "subversive" would have prevented the March 30 shooting. Knight, of the Secret Service, says it is impossible to determine now whether the service might have known about Hinckley if more domestic surveillance were going on.

John Simpson, an acting assistant secretary at the Treasury Department who supervises the Secret Service, said Treasury is working with the Justice Department on changing the intelligence controls. But he added that, "In this [Hinckley] case, I don't think it would have made any difference."

Actually, Congress has little to do with the Secret Service's access to domestic intelligence. The changes Knight wants to make involve a set of domestic intelligence guidelines issued in 1976 by Gerald Ford's attorney general Edward H. Levi.

Responding to national anger that followed reporting of the Federal Bureau of Investigation's treatment of allegedly "subversive" organizations -- treatment that ranged from illegal break-ins and unauthorized wiretaps to spreading false information about such leaders as Martin Luther King, Jr. -- Levi issued a set of rules that limited the FBI's right to follow, infiltrate and harass individuals and groups in the United States.

Knight has complained consistently about those rules. He says they have reduced by 60 percent the quantity of information coming to the Secret Service from the FBI -- although he admits that he cannot say whether the quality of the intelligence information has decreased as well.

In public committee sessions, at least, Knight has given no examples of particular kinds of information his agents would get if the guidelines were revised. And he specifically disagreed recently when a congressman suggested that better intelligence could have prevented recent attacks on presidents and other public figures.

Still, the Treasury Department's Simpson says the administration is already working on revisions to the Levi guidelines and that "some changes will definitely be made, although they may be minor."

Knight also said last week that he would like changes in the law dictating how many people the Secret Service has to protect. Currently, the service guards 20 people on a 24-hour, 365-day basis. "There are some people we are obliged to protect by law that in my opinion do not need Secret Service protection," Knight said.

In addition to Reagan, Vice President Bush and their families, the service protects Jimmy, Rosalynn and Amy Carter, Walter and Joan Mondale, Gerald and Betty Ford, Richard and Pat Nixon, Lady Bird Johnson and Bess Truman. Protection of the Mondales will terminate later this year, and Amy Carter will not be guarded after her 16th birthday.

Protection of Mrs. Truman, a 96-year-old resident of Independence, Mo., is considered the "Siberia" detail by some Secret Service agents because the president's widow gets round-the-clock protection even though she rarely leaves her home. One Secret Service official says that the only agents who like the Truman assignment are those working on advanced degrees, because the job gives them a lot of time to study.