India's Gandhi tries to keep ball rolling on regional issues. Longstanding differences with China and Pakistan are at the top of his list

Indian Prime Minister Rajiv Gandhi appears intent on seeking solutions to prickly regional issues. During his visit to New York to participate in the United Nations' 40th anniversary celebrations, Mr. Gandhi is hoping to meet with Pakistan's President Zia ul-Haq and Chinese Premier Zhao Ziyang.

India wants to set a favorable tone for future talks with its neighbors. The talks will likely focus on two critical questions:

Pakistan's nuclear weapons program.

India's border conflict with China.

Gandhi would like to meet with President Reagan to further improve US-Indian ties and seek US help in monitoring Pakistan's nuclear program. Gandhi is also attending a meeting of the Commonwealth in the Bahamas where he is scheduled to meet with Sri Lankan President Junius Richard Jayewardene.

With a new ceasefire agreement reportedly in place in Sri Lanka, Gandhi plans to ask the Sri Lankan leader to provide more concessions to Tamil militants who are demanding greater autonomy. If Gandhi succeeds in softening Mr. Jayewardene's stance and the ceasefire is maintained, talks could resume later this year between Sri Lankan officials and the Tamil groups.

In Indo-Pakistani relations, however, Gandhi may find it more difficult to make headway. Both countries have lived in deep-seated suspicion of each other since gaining independence from British rule in 1947. Aside from vague and tenative overtures, the two countries have barely inched toward friendlier ties, although both appear willing.

``We are willing to go to any extent . . . for normalization of relations with Pakistan, but [there are] limitations,'' Gandhi said recently.

The major stumbling block that poses the biggest security threat to the region is Pakistans nuclear program, India says.

Gandhi has often said that although he did not know exactly how close Pakistan is to making a bomb, he believes Pakistan's nuclear weapons program is ``fairly advanced.''

In India, Gandhi has to toe a careful line between asserting the government's peaceful use of nuclear power and appeasing a powerful domestic pro-nuclear bomb lobby. India tested a nuclear device in 1974 and the government says that its comprehensive nuclear development program is a ```peaceful'' one aimed only at producing energy. But, Gandhi says, if faced with absolute proof of Pakistan's nuclear weapons capability, India may be ``forced to reconsider'' the nuclear option.

Pakistan has repeatedly denied India's allegations. The US maintains that it has no definite proof that Pakistan has pursued a nuclear weapons project.

In a recent interview with an Indian magazine, General Zia was quoted as saying that ``Pakistan has acquired uranium enrichment capability not only for making a bomb, but for peaceful purposes.''

While this information could not be immediately confirmed, it may or may not provide additional grist for India's campaign.

The US has officially declined India's request for a monitoring program aimed at detering any Pakistani plan to build atomic weapons. But the US has increased pressure on Pakistan to improve relations with India, analysts say.

Gandhi wants to make the issue a matter of international significance. But the US is not prepared or willing to do so, analysts here say.

Apart from the nuclear issue, Gandhi will likely voice his continued concern over Pakistan's alleged assistance to Sikh terrorists across the border from Punjab -- India's strategically important state in the north.

In addition, fighting has escalated in the Indo-Pakistani battle for control of the Siachin glacier in northern Kashmir. India does not want to lose the area which overlooks the Karakoram highway linking Pakistan and China. India fears an alliance between Pakistan and China -- the two countries with which it has fought wars.

Gandhi's meeting with the Chinese leader will be a prelude to Sino-Indian talks scheduled for early November in New Delhi. Gandhi plans to touch on bilateral programs. Improving trade relations is one such program. India's allegation that China aids Pakistan's nuclear weapons program could touch a sensitive nerve.

But the border question is ``most central'' to relations which ``will take time to be resolved,'' Gandhi says. At the core of the dispute are the western and eastern parts of the Himalayan dividing line between India and China.

China has become more favorably disposed towards having better relations with India since Gandhi came to power and both countries have shown signs of wanting to reach some understanding during next month's talks.