A widely expected $300 million sale of U.S. M60 tanks to Jordan has been thrown in doubt by a competitive offer from Britain and by the strain in U.S.-Jordanian relations over the Egyptian-Israeli peace treaty.

King Hussein's increased willingness to consider British Chieftain tanks reflects irritation at restrictions imposed by the United States on the proposed M60 sale, as well as a vaguely defined suspicion here that Washington is using these restrictions to punish Jordan for its strong opposition to the treaty.

Authoritative sources said today that the monarch is expected to make his final decision soon. Purchase of the British tanks, following the king's recent agreement to buy 36 French F1 Mirage jets, would mark a clear setback for the U.S. role as Jordan's chief Western ally and arms supplier.

It also would be viewed as a symbol of the cooling between Hussin and the Carter administration because of Hussein's refusal to join the peace negotiations set up at Camp David in the March 26 peace treaty.

Another sign of the chill is a suggestion by the Soviet Union, relayed and pressed on Hussein by some of his Arab allies, that Jordan reject both the U.S. and British tanks and buy instead T72 tanks from Moscow, Jordanian and foreign sources said.

The Jordanian armed forces commander, Zeid Bin Shaker, visited Moscow in July, reportedly to discuss the offer. Hussein is considered unlikely to take it up, however, because of his traditional political ties to the West and the difficulty of shifting to Soviet equipment from the U.S. and European arms his officers are used to.

Observers here recalled that Hussein visited Moscow several years ago during a dispute with Washington over purchase of the U.S-made Hawk air-defense missile system, but that he finished by working out a compromise and buying the Hawks installed on immobile platforms.

The possibility remains that he could purchase some less important Soviet military equipment -- armored cars or trucks, for example -- as a sign of his closing ranks with such traditional Soviet allies as Syria, Libya and Iraq in opposition to the Camp David peace negotiations, observers here said.

The reconsideration of the M60 sale also follows Jordanian dissatisfaction at the United States' refusal to sell Jordan F16 jets to replace its aging and outgunned fleet of U.S.-made F5s.

Jordanian military planners were particularly eager to get an aircraft with night capability and "standoff" weaponry sophisticated enough to be a match for Israeli F15s, equipped with missiles that can shoot down an F5 from afar before its pilot knows the enemy is at hand.

Washington responded, however, that it was unable to supply F16s to Egypt's President Anwar Sadat, who is highly regarded in Congress for his peace policies, and so would be even less likely to supply them to Jordan, an opponent of those policies.

At that point, Hussein turned to France and agreed on the Mirage purchase.

The main point of contention concerning the tanks revolves around Washington's refusal to guarantee supplies of an ultrasophisticated night- sighting device. The infrared apparatus gives night capability to the $1.1 million M60A3 tank, the most advanced U.S. tank in production, with a 105mm cannon, a combat range of 310 miles and a top speed of 30 miles an hour.

The night device is among those weapons that under U.S. law must be specially approved for sale abroad.

What rankles the Jordanians, however is their conviction that Israel will soon get the approval and install the sight in its tanks.

Diplomatic sources here say Britain has told the Jordanian government it is willing to sell an equivalent night-sighting device along with the reported 250 Chieftain tanks it is promising to Hussein against the U.S. offer of up to 300 M60s.

The British offer also is unusually attractive because many of the Chieftain tanks are available for swift shipment. About 175 Chieftains produced for the Shah of Iran were left sitting in Britain when Iran's new revolutionary government canceled the sale.

These could be diverted immediately to Jordan if Hussein makes a deal with London. The monarch is expected to stop off in Britain on his way to address the United Nations at the end of this month, and this is likely to be one topic mentioned in his discussions with British officials.

The U.S. M60, on the contrary, is not ready for immediate delivery.

Some Jordanians are said to believe U.S. warnings of a long delay -- up to 30 months -- also reflect Washington's efforts to show unhappiness with Hussein's boycott of the Palestinian autonomy negotiations set up in the treaty.

The British Chieftain, regarded as a better tank by military experts, also is more expensive than the M60. Hussein has few money worries these days, however, with a prospering economy and pledges of $1.25 billion annually from his Baghdad summit allies lined up against Egypt.

Some reports here suggested the Jordanian military also was upset at U.S. requirements of a written pledge to get rid of one of the present fleet of M48 tanks for every new M60, thus ruling out an increase in the total armored fleet. Diplomatic sources contend, however, that Hussein never intended to increase his tank fleet, but has been interested all along in modernizing it.

The present fleet inclues an estimated 320 M48, M47 and already purchased M60 tanks, along with about 180 Centurion medium tanks.