When Imeld Romualdez married Congressman Ferdinand Marcos just 11 days after she met him in 1954, the impulsive young woman seemed destined to be little more than an unusually decorative political wife.

Now, as her husband begins his seventh year of one-man martial law rule over the 44 million people of this former American colony, there are growing signs that she will be named his successor. It is a prospect that angers Marcos' opponents and worries diplomats. But it does not surprise anyone who has watched Imelda Marcos' political performance over the last few years.

The first lady, now both a Cabinet minister and governor of greater Manila, has denied for weeks that she will be appointed to the new post of deputy prime minister, second only to Marcos, who serves a primes minister and president. But last week she called in a Filipino reporter working for a foreign news agency to say she might to accept the appointment and someday succeed her husband to save his "political legacy."

Although Imelda Marcos appears to be an energetic administrator, she is not as careful a politician as her husband and has generated some resentment here. She likes fine jewelry, all-night parties and shopping trips to New York while Marcos himself stops just short of being an ascetic. In approaching people she says, "The president thinks his way in: I feel my way in."

The thought of her heading the government bothers some American diplomats. they see her as an erratic personality who may not share her husband's personal commitment to the United States, forged when he fought alongside the Americans in World War II. Washington still is this country's principal ally despite Manila's growingly nationalistic foreign policy. For instance, the first lady recently suffered a minor disaster when, ill-prepared, she met U.S. congressmen in Washington and tried to finesse their complaints about the Marcos administration with pure charm.

Her effort to project the image of a private person reluctant to assume the reins of power also has begun to wear a bit thin here. Both she and Marcos have denied vigorously that she would be appointed deputy prime minister, but longtime observers noted that the couple had issued the same denials before she was selected as Manila governor and as leader of the pro-Marcos Manila slate in April's election for an interim National Assembly.

In an interview with Teodoro Benigno of Agence France-Presse last week, she acknowledged that she had now begun to change her mind. In the event of a difficult transition following Marcos' death or incapacity, "who else can the president rely upon to lead the Philippines during this stage except somebody very close to him?" she asked. She added: "I did not ask for this. I did not start this. In fact I was against it."

Marcos can make the appointment any time he wishes. He and his wife have had their occasional disagreements, and it is possible he is still worried about the adverse reaction from abroad and from his wife's domestic enemies to her appointment. He passed up a chance to make the announcement during his address on the anniversary of the Sept. 21, 1972, declaration of martial law.

But few people here are betting against the new title for the first lady. The outspoken opposition is attacking the appointment as if it has already taken place.

"A dynasty is against the democratic spirit, sensibilities, and wishes of the Filipino people," said a statement signed by a group headed by former president Diosdado Macapagal. "If his wife managed to succeed him despite the expectable conflict and bloodshed it will pave the way for her in due time to have on of their children become her successor."

The first lady prefers a more cosmic justification for her deep involvement in her husband's government: "We completely complement each other, like the yin and the yang."

The oldest of their three children, Imce, a recent Princeton graduate, has shown some interest in politics and now heads a national young group. But many people think it unlikely that the family could hold into power without Marcos himself there to weild his skill at keeping the archipelago's key military, economic and religious forces in balance.

Marcos declared martial law six years ago at at time of antigovernment riots, runaway crime and some reported attempts on his life. He muzzled what was once the most antigovernment press in Asia and still rules by decree; despite the recent election of a National Assembly that was supposed to assume some of his legislative powers.

His worst problem is a bloody war against southern Moslem separatists, whom he has tried to buy off. he keeps his most attractive political opponent, former senator Benigno Aquino, in jail. August McCormick Lehman, an American who confessed to being the triggerman in a plot to kill Marcos, was recently pardoned, however, to encourage other Marcos opponents to see the light. Lehman married the daughter of one of his jailers, expressed his loyalty to Marcos and has been set up in Manila export business by Marcos' intelligence chief, Maj. Gen. Fabian Ver.

Marcos celebrated his 61st birthday Sept. 11, still vigorous, youthful-looking and apparently healthy. Although his wife is reluctant to give her age, government press aides say she is 49. She also appears to be in good health, totally recovered from a 1972 assassination attempt that left severe cuts in one arm.

Imelda Marcos' relatives hold several important positions in government and business here. Development projects across the country bear her name in large letters. Marcos has used her on several delicate trade and diplomatic missions.

She appears to have an almost limitless confidence in her own ability to win people over by pure force of personality, such as this week when she won a smile from dour Vietnamese Premier Pham Van Dong by singing a few Philippine folk songs.

In a Philippine magazine interview comparing herself to her husband, she said, "I just take it for granted that everybody wants me. I start with the premise that everybody loves me. He starts with the premise the maybe nobody cares."