"No President, however farsighted and decisive, can now conduct an effective foreign policy."

Honestly, that's what Boston University president John Silber flatly declares in The New Republic magazine. His elaboration of the theory is equally categorical: It's Congress' fault.

"Ever since the War Powers Act of 1973, the separation of powers has been compromised," he writes. By adding all sorts of restrictions to American aid, he argues, Congress has further robbed the president of "essential freedom of maneuver" to deploy American forces or to assist insurgencies. It has also stripped away the secrecy necessary for unacknowledged, covert operations. It has "institutionalized Neville Chamberlain as the model for American Presidents."

Silber's case is not entirely wrongheaded. The requirements imposed upon the president by the War Powers Act may well have been too rigid a reaction to Vietnam. The "oxymoron" as Silber puts it, of open congressional debate on "covert" activities in Nicaragua may be an overreaction, as well, to the 1970s expos,es of earlier CIA malpractices. Silber is on to a real problem. And his solution is widely shared by appointed policy makers, academicians and others happily unencumbered by the commands of elective office.

Congress, of course, must be "informed" and "consulted." But Congress must provide "leadership rather than politically motivated second- guessing." This means "looking beyond the next election and pursuing a course that is, in the longer run, in the national interest."

None of this, naturally, is to argue that Congress "should not help determine our foreign policy . . . the objectives of our foreign policy must be an expression of our nationa will." So what Silber seems to be saying is that there must be no second-guessing by the people's representatives, even if bungled operations or fatally flawed enterprises bring about a change in the national will.

Silber, in short, is no clearer in his head than most of us who find it increasingly difficult to draw that fine line between executive and legislative power in a nuclear age when power struggles are conducted by subversion, terrorism and other forms of undeclared war. Where he differs with most of those grappling with this problem is that he lays it all off on Congress.

The War Powers Act is sufficiently questionable on constitutional grounds to justify a second look -- if not a thorough review. But its repeal would not solve the problem. Silber shudders at what might have happened if it had been in effect when Truman set out to rescue South Korea or when Lyndon Johnson sent the Marines into the Dominican Republic. But he fails to note that it did not stop Ronald Reagan from doing his thing in Grenada and neither did it stay his hand in Lebanon.

The solution is not in lifting this or that congressional restraint. Congress would still be free to impose the power of the purse on the president's foreign policy. Circumstances would continue to alter cases and the real answer would continue to rest with states of mind -- public opinion, the congressional response to it and the attitude and conduct of the executive.

As we discovered in daily dispatches from the CBS-Westmoreland libel trial, those were not imagined offenses on the part of the executive that Congress was trying to deal with in the War Powers Act. We got hard evidence of the way the Johnson administration in 1967 was concealing the size of enemy forces, exaggerating "body counts," and otherwise doing its best to artificially inflate the appearance of progress. Johnson had his reasons. Not only was his own popular support sagging and his reelection deadline only a year away, but public support for the war was flagging. And public support was the key to the whole strategy of limited war.

What this says about the ability of an open society to pursue unconventional wars, where progress is not measured by the ebb and flow of front lines and objectives are limited to negotiated settlements, may well be one of Vietnam's lessons. Whatever the case, this recent evidence of how fast and loose the game was played by the executive branch ought to put an end to the notion that congressional handcuffs are the only way that the constitutional separation of powers can be compromised.