The commander of the British naval task force sent to regain the Falkland Islands from Argentina indicated last night that some of his ships would be within striking distance of the islands by this weekend.

Adm. Sandy Woodward said he had ordered the lead ships of the task force, believed to include at least 28 military ships and 35 civilian vessels strung out over 7,000 miles of the Atlantic Ocean, on alert status beginning midnight Friday.

The admiral told a British reporter in an interview aboard the aircraft carrier Hermes that he had issued the order because the task force would come within striking range of Argentine aircraft by Friday night. Argentina's Mirage fighter-bombers have a combat radius of about 700 miles. There are at least two air bases on the Argentine coast, but it is unclear if any jets have been based on the Falklands.

Woodward's order came amid indications that time was running short for a negotiated settlement of the crisis with the arrival of British Foreign Secretary Francis Pym in Washington for crucial talks with Secretary of State Alexander M. Haig Jr.

On a late-night television panel, Deputy Foreign Secretary Douglas Hurd said the crisis had entered a "new phase." Discussing possible military options, he said, "Difficult decisions will have to be made next week."

British and Argentine aircraft made contact for the first time yesterday when a Harrier jet aboard the Hermes intercepted an Argentine Boeing 707 plane apparently scouting the British fleet.

"We were almost touching wingtips," said pilot Simon Hargreaves, before the 707 returned to the mainland. Hargreaves was under orders not to fire.

The task force reported a second Argentine reconnaissance flight early Thursday morning, United Press International reported from the Hermes. British officers said the plane was chased off by a Harrier jet before it got within 30 miles of the British ships.

Woodward said he planned to impose an air blockade to go along with the sea blockade Britain has imposed for a radius of 200 miles around the Falklands. But British sources said they had no knowledge of the plan and that such an order would have to be made by the government here.

Nevertheless, an aerial blockade is regarded by a number of informed sources as the most likely next step in escalating British military pressure on Argentina.

A Defense Ministry spokesman here also sought to disavow Woodward's statement in the interview that the Argentines would be allowed the first shot in an engagement. Two weeks ago Defense Minister John Nott said that within Britain's declared war zone, "we shoot first."

The ministry spokesman today said, "As the task force moves further south the rules of engagement will be kept under political review."

In a television interview, Woodward characterized the present war of nerves as "a game of bluff and double bluff." He went on to warn the Argentines, "Don't take us on because you will lose," and gave odds of 20 to 1 in his favor.

"I'm not one for blowing people's heads off at any time if I can avoid it," he said, adding, "If my job is to blow people's heads off, I'll do it in the most efficient, effective way I have to."

Observers here saw Woodward's remarks as part of the psychological warfare game the British military has been playing with Argentina.

Military officials have refused to provide any information on the whereabouts of the task force or when it will arrive in the vicinity of the Falklands. But Woodward's remarks suggested that the Hermes and other lead ships are probably less than 1,000 miles from the islands. It is believed that the convoy can sail at about 15 knots, meaning that the lead ships could reach the islands by next Monday.

Observers have suggested, however, that the ships may be sailing at "diplomatic" speed to give negotiations more time.

The Defense Ministry has named 28 military ships in the task force and spokesmen will say only that "there may be more." The 28 include two aircraft carriers, two assault ships, two cruisers, five destroyers, five frigates, five landing craft and seven tankers and support ships.

The task force is reportedly carrying 1,500 Marines, who would serve as the primary assault force, and 2,500 paratroopers, who would be used for longer-term operations if the Marines are successful in retaking the islands. The force is expected to be supplemented by two ferries carrying helicopters and about 1,000 paratroopers leaving British ports this weekend.

No official information is available on the submarines patrolling the 200-mile war zone although there are believed to be four on station.

Aside from 20 Harriers aboard the lead ships, 20 more are en route. With refueling, they are capable of covering a 1,500-mile combat radius and although slower than Argentina's Mirages, they are more maneuverable.

There are also 37 antisubmarine helicopters and five used for transport.

There was more speculation today that the task force's first military target may be recapturing the barren, virtually uninhabited island of South Georgia, 800 miles east of the Falklands.

It is believed that there are no Argentine warships in the vicinity and only about 100 troops on the island, which was taken shortly after the Falklands following a firefight with British Marines.

In answer to a question in Parliament today, Prime Minister Margaret Thatcher called South Georgia "extremely important." The government has repeatedly refused to confirm or deny that part of the task force has broken off to head for South Georgia, which is slightly larger than Rhode Island.