The United States and Pakistan ended two days of inconclusive discussions here yesterday about the South Asian nation's drive to produce highly enriched uranium suitable for an atomic bomb.

Following a final round of talks late yesterday afternoon between Secretary of State Cyrus R. Vance and Pakistani Foreign Affairs Adviser Agha Shahi, the U.S. side reported that no specific decisions had been taken, and none had been anticipated.

Shahi, who is the ranking Pakistani foreign affairs official behind President Mohammed Zia ul-Hag, said that differences remain between the two countries after the lengthy discussions on the nuclear issue.

Informed sources on both sides gave no indication that a breakthrough had been reached or even approached.

Both sides made it clear that discussion of the issue will continue at a high level in the two governments.

The United States terminated economic and military aid to Pakistan last April under a nonproliferation law that requires such a cutoff when nations import equipment and technology, outside of international safeguards, that can be use to make atomic bombs.

The action was taken after U.S. intelligence confirmed reports that Pakistan is building a high technology plant near Islamabad to produce highly enriched uranium that could be used in an atomic bomb. Much of the equipment and technology for the plant, which is not needed to support Pakistan's small nuclear power program, was acquired in Europe through clandestine means.

In order to restore Pakistan to eligibility for U.S. aid, President Carter would have to certify that he has "reliable assurances" that Pakistan will not "acquire or develop" atomic weapons or assist other nations in doing so.

Shahi said Pakistan has given such assurances to the United States. However, indications are that the United States does not consider the assurances reliable or solid enough while work on the secretly assembled uranium plant continues, without international inspection or safeguards.

Shahi refused to confirm or deny a press report that work has stopped on the uranium plant. U.S. officials said as the talks convened that they have no information to back up the report.

Among the items discussed in the Vance-Shahi talks, in which several other high-level officials participated, was the security situation of Pakistan and its need for assistance to upgrade its military forces. The need is underlined by growing Soviet presence and influence in neighboring Afghanistan, where civil war is continuing.

Members of Congress and some Carter administration officeials have suggested that Pakistan be offered new military aid or sales to enhance its security in return for stopping its enriched uranium program. It could not be learned if such a proposal was broached to the Pakistanis in the talks here.

While the talks in Shahi were taking place yesterday, the State Department reacted sharply to Tuesday's announcement from Zia that he has tightened marital-law control on the country and postponed indefinitely the long-promised elections scheduled for next month.

Spokesman Hodding Carter said the United States is "deeply disappointed" at the actions, which postpone a return to civilian rule. Zia took power in a military coup in July 1977 from Zulfiquar Ali Bhutto, who was executed in March after confiction on murder and conspiracy charges.