Twenty years ago, she was a hawkish housewife, preoccupied with raising three children and suffering no ambivalence in her support for the American war in Vietnam.

Today, after one of the most remarkable ascents in American political history, Geraldine A. Ferraro is in a very different world. The Democratic vice-presidential nominee warns of a deepening American involvement in Central America, ponders the merits of the MX missile versus the Midgetman missile and decries the nuclear arms race.

In a wide-ranging interview earlier this week on topics ranging from the 600-ship Navy to the influence of Roman Catholicism on her world view, Ferraro acknowledged that national security "is not my strongest suit." She conceded that "a good portion" of what she now knows has been learned during campaign tutorials in the last several months.

Ferraro also admitted that her credentials are "not sufficient to make me secretary of defense this week," -- then added with a laugh, "Maybe next week."

Yet she vigorously defended herself as "having more than a sufficient amount of knowledge to match the president's knowledge."

"I have not been to 57 countries as Vice President Bush has, but I have been to . . . the Middle East and Central America," she said. "I know that I would not go to the Philippines as did Bush and raise my glass to President Ferdinand E. Marcos to toast him as a great defender of democracy.

"Do I know everything there is to know about everything? No. But neither do any of the other candidates. Maybe, Fritz Mondale does. He's the only one who does."

At times she seemed determined to appear tougher than President Reagan, insisting, for example, that on "numerous" occasions the Soviets have violated arms-control agreements with the United States and that "to sit by and not push for enforcement of the treaties when there've been violations is outrageous."

Among Ferraro's other statements:

*She said "it would be no threat to us" if Nicaragua suddenly introduced high-performance, Soviet-built MiG fighter planes into Central America -- unless "you see the Soviet Union putting a base in there, with MiGs being piloted by Soviet pilots" rather than Nicaraguans. Yesterday, Ferraro summoned a reporter to the front of her campaign plane to add that any MiGs in Nicaragua "are a concern obviously because they're the newest technology which would put the Nicaraguans at a position of superiority to their neighboring countries as to the equipment they would be using."

* In the original interview, she agreed that "there are circumstances" -- perhaps when there are egregious human-rights violations -- in which it would be appropriate for the United States to work covertly to overthrow a foreign government. However, she deplored the U.S. covert war in Nicaragua and strongly emphasized that, in general, "overthrowing governments is not an activity for the United States."

*She would consider reversing her opposition to the MX intercontinental ballistic missile if a different basing mode were contemplated. Ferraro voted for the MX in 1980 in the House when Defense Department strategists wanted to move the missiles around a "race track." She contends that the current plan to put the missiles in hardened silos makes them too vulnerable to attack.

*She said she does not "think it's necessary" to have on-site inspections of Soviet military facilities as part of an arms-control agreement. "I don't believe we trust the Soviet Union," Ferraro added. "I wouldn't sign an arms-control agreement unless it was verifiable . . . . You don't include that weapon or that weapons system or whatever in the treaty" unless the United States is certain of compliance.

*A "quarantine" of Nicaragua, as Democratic presidential nominee Walter F. Mondale proposed last month if the Sandinista government "uses any force outside of its borders," would be "a second or a third or a last resort" to be contemplated if negotiations fail, she said.

The interview with Ferraro took place on the back patio of her middle-class house in Queens, N.Y. With typical Ferraro panache, she jokingly turned at one point to show her back when the subject arose of whether she "had the backbone to launch a retaliatory nuclear attack."

Growing somber, Ferraro warned the Soviets of "swift and precise and certain" retaliation, while suggesting that such "finger-on-the-button" questions are asked more pointedly of her because she is a woman. "I think they never ask that of Vice President Bush," she added.

Later, she interrupted the interview to greet her son, John, 20, with a hug and promises of imminent dinner.

In general, Ferraro gave concise, self-assured answers to broad policy questions, turning to consult with foreign policy adviser Madeleine K. Albright twice on minor points. On more specific, technical questions, she occasionally was vague and groping.

The suspicion that Ferraro lacks sufficient mastery of national security issues stems, in part, from a stereotype that a woman with six years' service in Congress and a stint as a local prosecutor cannot have mastered the arcane aspects of foreign policy.

The candidate, however, also has contributed to the doubts, as when she said in an interview before her nomination, "Give me weapons and I don't know one from another." In Kansas City last month, she also appeared to confuse the nuclear doctrine terms "first use" and "first strike."

When it was pointed out that she has called for a mutual, verifiable moratorium on antisatellite (ASAT) weapons, Ferraro acknowledged that she could not describe in layman's terms how the system is supposed to work.

"God, this is like a test!" she exclaimed. "We currently have a satellite which has been tested. Well, ours is the newest model. The Soviets do have an antisatellite weapon which has been tested. How does it do it in layman's terms? It is able to deal with satellites, low satellites, not the high satellites that are doing our intelligence gathering. . . . How specifically does the U.S. weapon work? No."

One of Ferraro's main strengths as a candidate is her ability to articulate her deepest concerns. Her strategists argue that technical information is being learned -- "quick study" is the phrase usually applied to Ferraro by her aides -- but that vision and conviction are inherent and paramount.

"Like every other parent, I did not raise my son and daughters to die in an undeclared war against an unnamed enemy for an uncertain cause," she said during a rally in Oakland this week.

Ferraro said she didn't know whether her views on Vietnam are shaped by her gender because "there are so many men who feel the way that I do." At first, "like all of America, I was behind" President Lyndon B. Johnson on Vietnam but eventually grew disillusioned, as did the country, when "I saw us getting more and more involved, not having a way out of it."

On other issues, Ferraro said in the interview that she would scrap the Reagan administration's plans to relocate urban dwellers to rural areas if a nuclear attack is threatened.

Ferraro said she supports current American troop levels in South Korea and Western Europe.

Turning again to Central America, she said, "The similarities between Central America and Vietnam are not many. But where they exist, it's a little bit frightening. At the very beginning we only had a number of advisers in Vietnam. Then after a couple of years we started sending money for military assistance. When you see that happening in Central America, you begin to worry if you're going to be on the same plane, the same level."

Asked what had influenced her thinking about how the United States should behave as a global power, she said:

"Perhaps at the risk of getting involved in this subject, my religious upbringing as well as the way I've gone through life. Again, I've treated people fairly, I expect them to treat me fairly.

"I think you do that not only in your own home with people that you love, but you do that in your neighborhood, in your country, you do it in the world. That's what life is about."